Thermally-driven phase transformation in high temperature structural materials has great influence on its service performance. Phase transformation of the main constituent phases (i.e. (Nb,Ti)ss and Nb5Si3) of Nb-Ti-Si based alloys, as promising candidates for turbine blades, have been fully understood. However, microstructure evolution of interfacial precipitates upon heating is still uncertain. In this paper, transformation process of interfacial Ti precipitates in heat-treated Nb-Ti-Si based alloys is systematically investigated by in-situ high-resolution transmission electron microscopy (HRTEM) observation. The hexagonal-close-packed Ti (hcp-Ti) lath martensites precipitated from bulk face-centered-cubic Ti (fcc-Ti) in heat-treated alloys reversely transform into fcc-Ti laths during heating. Two periodic structures nucleate and act as modulated structures in the process of hcp-Ti to fcc-Ti reverse martensitic transformation. The transformation proceeds from interior area to the sharp interface of an hcp-Ti lath through formation of growth ledges. Our findings provide a comprehensive insight of structural phase transformation of Ti, suggesting that the overall structural stability of Ti decreases in the following order: hcp > periodic structures > fcc.

One dimensional nanostructures have the prospect to change the properties of materials used in contemporary devices. Recently we reported a process to grow perfect defect and flaw free nanostructures with diameters of several ten nanometers under UHV conditions. Typical diameters of the nanowhiskers are 100 nm and lengths of up to 50 µm are observed.Co shows two allotropes, a room temperature hcp crystal structure and above 420°C a stable high temperature phase of hcp structure. For nanoparticles the fcc phase is seen repeatedly. This can be explained by the increasing effect of the lower surface energy for the fcc phase compared to the possible hcp low indexed surface crystal planes. Since the enthalpy of transformation is small, the surface energy contributions lead to a size effect in the crystal structure.In the presentation we will address the growth of Co nanowhiskers and the onset of the fcc-hcp phase transformation in those nanostructures as a function of temperature as observed in situ a high resolution, high voltage transmission electron microscope. We will address the microstructure of the Co nanowhiskers. Compared to the perfect crystal structure of fcc nanowhiskers, those grown for Co exhibit stacking faults parallel to its axis when observed at room temperature. The overall crystal structure is fcc, however the stacking faults can be considered as local hcp structure. In situ heating and cooling experiments were carried out with the goal to reach the stable hcp crystal structure in Co nanowhiskers. During thermal cycling partial dislocations are nucleated and propagate on {111} planes, again forming only a local hcp structure. The overall fcc crystal structure however remains seen down to temperature of -160°C. The geometry and microstructure has implications on the magnetic domain structure of the nanowhiskers, this will briefly reported.

Elucidating the resistive switching behavior of binary oxide nanostructures involves gaining an understanding of how the changes in transport behavior are correlated with local changes to the structure and composition of the oxide. We have explored a number of binary oxides including NiO, CuO and TiO2 and we will present data that show how correlating different X-ray, electron and scanning probe microscopies will modeling can lead to a fuller understanding of the transport behavior. We will present in situ TEM studies of the electroforming and resistive switching behavior of Pt/NiO16 nm/Pt heterostructures, in which the variation in microstructure of adjacent NiO regions, with a width of ~ 300 nm, lead to local variations in resistive switching behavior. The resistance change could be ascribed to the formation of conducting pathways during in situ TEM biasing, in which ordering of oxygen vacancies occurs [1]. We will further present results of experiments carried out at the APS on TiO2 films, in which a novel photovoltaic effect induced by the incident X-ray beam led to a volatile change in resistance, with a subsequent non-volatile effect induced by the formation of conducting pathways across the irradiated area, observed using conducting AFM, and identified as Ti4O7 from cross-section HREM images [2]. Finally we will discuss the use of X-ray fluorescence microscopy at the nanoscale to explore the electroforming behavior in CuO thin films.

This work was supported by the U.S. Department of Energy (DOE), Office of Science, Materials Sciences and Engineering Division. Use of the Center for Nanoscale Materials, and of the Advanced Photon Source, which are Office of Science user facilities, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Anisotropic metal nanoparticles, and especially nanorods (NRs) exhibit interesting optical properties, which arise from their strong localized surface plasmon resonance. Unlike nanospheres, gold NRs have a longitudinal surface plasmon resonance in the visible or near-infrared range of the spectrum, which makes them interesting materials for a broad range of light based applications, such as photocatalysis [1], data storage [2], surface enhanced Raman spectroscopy (SERS) and photothermal applications. The plasmonic and (photo)catalytic properties of gold NRs can be modified by introducing a second metal. However, synthesizing and characterizing bimetallic NRs with a good control over the metal composition and distribution while retaining the rod shape is challenging.

In this study we demonstrate the synthesis of core-shell-shell NRs with an Au-core, Ag, Pd or Pt metal inner shell and mesoporous silica outer shell [3]. We show that it is possible to synthesize such core-shell-shell nanoparticles with a precise control over the metal-to-metal ratio, and characterized the NRs in detail using advanced electron microscopy techniques such as Energy-dispersive X-ray spectroscopy (EDX), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron tomography. Subsequently, we used the core-shell-shell structured rods as a starting material to make alloyed NRs, whereby the two metals were mixed via thermal treatment without loss of anisotropy [4]. The alloying process was followed on a single particle level with in-situ HAADF-STEM and EDX measurements by making use of a special heating holder, and on an atomic level with in-situ extended x-ray absorption fine structure (EXAFS) measurements. Both core-shell and alloyed bimetallic NPs with a well-defined metal-to-metal ratio and particle shape are desirable model systems for catalysis.

The inception of graphene and voluminous research investigating this promising two-dimensional (2D) material has spurred the exploration of similar 2D systems. 2D layers of transition metal dichacogenides (TMDC) have gathered interest due to their semiconductor band gap opening potential applications in optoelectronics and electronic devices. As the TMCDs are only a few atoms thick, atomic defects have been demonstrated as a powerful strategy to control their electronic band structure, therefore it is essential to understand the nature of the atomic defects in TMDC to engineer them into a device system. Aberration-corrected transmission electron microscopy (AC-TEM) has been demonstrated as a suitable technique to survey these atomic defects, because of its capacity to visualize atomic structure of 2D materials and to modify the atomic structure by electron beam irradiation.

In this work, we studied the formation and migration of atomic defects in MoSe2 on graphene using AC-TEM to explore defect behavior in van der Waals (vdW) heterostructures. The MoSe2/graphene vdW stacked heterostructure was prepared by a direct growth of MoSe2 on CVD graphene, thereby attaining an ideal vdW interface between the two 2D monolayers. During in situ electron irradiation, point and line defects are generated in the MoSe2 layer. The line defects were identified as single and double vacancy line defects by comparison with structures simulated with density function theory (DFT). Under continuous electron irradiation, the line defects are mobile within the MoSe2 layer, and form larger chains or accommodate for neighboring defects. The formation and migration of defects in MoSe2 caused local displacement and strain in the vdW heterostructure. The signals from MoSe2 and graphene monolayers were decomposed using fast Fourier transform based image filtering and independently analyzed, which enabled monitoring the relative atomic positions and strain propagation from the MoSe2 to graphene. The MoSe2 layer was observed moving on the surface of graphene layer during the formation of point and line defects within the MoSe2 layer. The individual movement of MoSe2 on the graphene surface indicates that we are able to independently modify the MoSe2 atomic structure in vdW heterostructures, which could be utilized for device processing. Finally, we also investigated the intrinsic defects in synthesized MoSe2, their evolution amid growth processing steps, and their influence on the formation and movement of extrinsic defects.

The ‘phase space’ for materials discovery is much larger in system far from equilibrium due to the large number of metastable phases that can be accessed. Understanding and controlling phase and morphological selection for the numerous metastable phases requires probing the details of the atomic scale processes. Accomplishing this requires better integration of experimental and characterization tools with the development of theoretical methods that can account for non-equilibrium driving forces and kinetic effects. State-of-the-art aberration corrected scanning transmission electron microscopy (AC/STEM) provides the requisite chemical and spatial sensitivity; however in operando studies also require precise temperature control and positional stability during data acquisition. Using the FEI NanoExTM-i/v MEMS microheater in a FEI Titan Themis 300 Cubed 300 STEM we have been able to precisely measure the nucleation and growth of metastable phases and the atomic scale attachment kinetics of an amorphous binary alloy. Subsequent solid-solid phase transformations were likewise characterized. This is accomplished, in part, by employing a series of heating/cooling cycles of the sample where the positional reproducibility is within a few nm and the temperature variability is < 0.1 K. This allows for precise measurements of interface mobility, solute segregation, and coupled growth involving nanoscale defects which were only revealed by direct observations. Challenges and opportunities for such detailed studies will be discussed, including the effects of sample preparation on the observed phase selection process.

This work was performed under the auspices of the U.S. Department of Energy, Basic Energy Sciences, Ames Laboratory Contract No. DE-AC02-07CH11358.

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10:30 AM - *TC02:01.07

In Situ Observation of Shear-Driven Amorphization Process in Silicon Crystals

Scott Mao 1 1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

This talk will be based on recent publication on Nature Nanotechnology by Yang He, Li Zhong, F. Fan, Chongmin Wang, Ting Zhu and Scott X. Mao. Amorphous materials are used for both structural and functional applications. An amorphous solid usually forms under driven conditions such as melt quenching, irradiation, shock loading or severe mechanical deformation. Such extreme conditions impose significant challenges on the direct observation of the amorphization process. Various experimental techniques have been used to detect how the amorphous phases form, including synchrotron X-ray diffraction, transmission electron microscopy (TEM) and Raman spectroscopy, but a dynamic, atomistic characterization has remained elusive. Here, by using in situ high-resolution TEM, we show the dynamic of the amorphization process of silicon nanocrystals during mechanical straining at the atomic scale. We find that shear-driven amorphization occurs in a dominant shear band starting with the diamond-cubic (dc) to diamond-hexagonal (dh) phase transition and then proceeds by dislocation nucleation and accumulation in the newly formed dh-Si phase. The process then leads to the formation of an amorphous Si (a-Si) band, embedded with dh-Si nanodomains. The amorphization of dc-Si via an intermediate dh-Si phase is a previously unknown pathway of solid-state amorphization.

11:00 AM - TC02.01.08

Direct Observation of the Reaction Mechanism of Ni/6H-SiC and Behavior of Carbon at Low Temperature by In Situ Transmission Electron Microscopy

Silicon carbide (SiC) is known that it used commonly for efficient high power application. Especially for the electric device, Ni / SiC contact is important because of their chemical, thermal stability and low electric resistivity. Many studies on the reaction have been reported but they are mostly result of ex-situ or in-situ x-ray diffractometer at high temperature or long annealing time. Therefore, the mechanism of initial reaction and carbon diffusion behavior is currently insufficient. To control appropriate variables for using device, it is necessary to understand the mechanism of initial reaction state. In this study, we investigated the reaction of Ni films on 6H-SiC substrate at low temperature and observed behavior of carbon through in-situ heating TEM. At 550 °C, Ni31Si12 phase was formed during reaction of Ni and SiC. Ni-silicide layer progressed to the 6H-SiC substrate and carbon atoms decomposed from SiC were changed graphite. Also, region where carbon exists can be divided into three. First, carbon was existed graphite on external surface of Ni-silicide layer and second, graphite was in initial interface between Ni film and 6H-SiC substrate. Finally, carbon existed in bottom Ni-silicide area due to low diffusivity in silicide. Through EDS line profile and EELS mapping, the distribution of Ni, Si and C were observed in detail. We demonstrate the mechanism Ni and SiC at 550 °C and distribution of carbon atoms.

11:15 AM - TC02:01.09

How a Cation Exchange at Solid State between Diverse Nanoparticles Populations Occurs—New Insights by In Situ HRTEM and STEM-EDS Imaging

A cation exchange (CE) is defined as the partial or complete replacement of a cationic species in a crystalline structure, leaving the anionic lattice unmodified. CE is usually made at the liquid state between inorganic colloidal nanoparticles (NPs) and a cationic species, but this environment and the CE reaction fast kinetics impede the direct imaging of the cation replacement phenomenon while it is occurring. However, in the recent past we showed that the use of an in situ TEM/STEM/EFTEM approach with reactants at the solid state provides a method to overwhelm these limitations. [1] In fact, we showed how, once heated, spherical Cu2Se NPs with cubic crystalline phase are able to expel free Cu species, forming Cu-vacancies in the cation sublattice with subsequent variations in their stoichiometry (up to about Cu1.8Se). Such a thermally-driven expulsion of free Cu species has then been exploited to perform in situ CE reactions at the solid state between the cubic Cu2Se NPs and CdSe nanowires (NWs) deposited on a common heated substrate. When reached by the free Cu species, CdSe NWs suffer general and concomitant chemical and structural transformations, with the substitution of any Cd atom by two of Cu. As a consequence, Cu2Se constitutes the final, completely substituted NWs. However, while in the past we showed how this phenomenon occurs at 400 °C for starting CdSe NWs with hexagonal crystalline phase [1], recently we have found further and unexpected insights about how the phenomenon actually occurs. First, we demonstrate its feasibility even for NWs with cubic phase, but in such a case the activation temperature is lowered down to less than 150 °C. This means that this temperature, acting as a threshold for CE, is strongly dependent on the crystalline phase of the CdSe cations-acceptor nanostructures: given the higher energy required to complete the hexagonalàcubic CE-induced phase transition in the case of exchanging hexagonal CdSe NWs, their activation temperature has been found higher, as well. Second, we disclose that the copper expelled by the Cu2Se NPs, before entering the CdSe NWs and giving rise to the CE reaction, surrounds the NWs forming a sort of cylindrical thin layer and, once into the NWs, it moves along their length with different speeds in the two opposite directions. Thus, the application of the in situ HRTEM and STEM-EDS heating, combined with the slow kinetics of CE reactions at the solid state, allows the direct and finely detailed imaging of the transient states leading to the reaction’s completion, which conversely would be the only observable step in case the same phenomenon occurred at liquid state.

Two-dimensional materials provide opportunities to directly observe atomic-scale defect dynamics. A direct exchange between a substitutional impurity and a neighboring host atom has been discussed in the literature, but the energy barrier for such a process is generally believed to be too large. No atomic-scale observation of direct exchange events has been reported. Here we use scanning transmission electron microscopy to observe substitutional Re impurities in monolayer MoS2 undergo direct exchanges with neighboring Mo atoms. Density functional theory calculations find that the energy barrier for direct exchange is too large for either thermal or beam-induced exchange. Microscopy further reveals the presence of an ever-changing number of S vacancies, but the calculated energy barrier remains too large to account for the jumps. The calculations further find that a Re impurity and surrounding S vacancies introduce an ever-changing set of localized levels in the energy gap. We propose that these levels mediate an “explosive” recombination-enhanced migration via multiple electron-hole recombination events. Our experimental and theoretical findings lay a fundamental framework towards engineering substitutional dopants in two-dimensional materials. The present work has clarified the energy transfer mechanism between the electron beam and layered semiconductor materials, laying the foundation for future work towards manipulating single atoms using an electron beam.

The oriented attachment of molecular clusters and nanoparticles is a commonly reported mechanism of crystal growth in many materials, yet the microscopic mechanisms associated with the alignment of nanoparticles during coalescence has not been established. We studied the coalescence of prototypical gold and copper nanoparticles using in situ electron microscopy coupled with atomic level simulations. In contrast to the oriented attachment hypothesis, the alignment of nanoparticles after contact is driven by extensive dislocation activity irrespective of the initial misorientation of the particles. Rapid dislocation aided alignment during coalescence is followed by twinning or surface diffusion aided neck growth and subsequent surface diffusion aided shape evolution. In contrast to microcrystalline particles, we found that with thermal fluctuations grain boundaries at the interface between two particles readily disintegrate, or migrate to the surface thereby leaving behind a defect-free single crystal. The fact that many nanoparticles with different orientations coalesce to form single crystal aggregates suggests a revision of the scope of oriented attachment during crystal growth by nanoparticle aggregation. This dislocation aided alignment of nanoparticles followed by surface diffusion aided shape evolution is very different from the classical picture of sintering of microcrystalline particles.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

An understanding and ultimately controlling of the materials dynamic processes at liquid-solution interfaces is important for a variety of applications including solution based synthesis, solar to fuel energy conversion and storage, materials corrosion and others. We study materials dynamic phenomena by developing and applying liquid environmental cell transmission electron microscopy (TEM) and other complimentary methods. In this talk, I will show the revealing of nanocrystal growth in solution, including noble metal nanoparticle growth and assembly, transition metal oxide formation and shape evolution with liquid cell TEM. Assisted with Density Functional Theory calculation, the energetic barriers for materials transformations and ligand effects are achieved. The direct atomic level observation in combination with theoretical calculations allows a depth understanding of organic ligand mediated inorganic nanomaterials formation and transformations in solution.

2:00 PM - TC02.02.02

Expanding Environmental Control with New Nanofluidic Platforms for Liquid Cell-(S)TEM

Liquid Cell Transmission Electron Microscopy (LC-TEM) has enabled dynamic visualization of phenomena at the nanoscale from disciplines ranging across energy, biology, and medicine. While the barrier of entry has been significantly lowered in recent years with the availability of commercial holders, experimental flexibility and reproducibility remain limited. Liquid cell thickness variability across serial experiments can affect contrast and resolution between experiments and additionally influences the interaction volume and growth kinetics of growth experiments using the electron beam as a reducing agent. The limited imaging area of a single window device can also constrain the number of imaging experiments which can be performed before changing samples. Additionally, the inability to route flow directly to the imaging area can result in a significant portion of the sample flowing around, rather than in between, the silicon devices used for LC-TEM imaging. Such bypass of flow can artificially select or filter the sample of interest or create unknown chemical gradients at the imaging area.Here, we detail advances to LC-TEM instrumentation which are designed towards overcoming the limitations described above. Design is rooted in the need for controlled generation of repeatable LC-TEM environments which can produce results with statistical power. We also highlight future planned advances to gain even greater control of the LC-TEM mixing environment for complex chemical reactions.

Acknowledgements: Work was supported by DOE-BER Mesoscale to Molecules Bioimaging Project FWP# 66382. A portion of the research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at PNNL.

Pitting corrosion is a form of localized corrosion which creates surface flaws that lead to crack initiation in operation. Though such pits are common on passivating metals such as aluminum and stainless steel, the mechanism of pit initiation is still not well understood. Our goal is to image such nucleation events in real time in a Liquid Cell in the Transmission Electron Microscopy (TEM). However, Liquid Cell TEM introduces an additional variable in the corrosion cell environment; energetic primary electrons which have the potential to generate radiolytic products in the liquid through generation of secondary electrons, which can thereby influence the microstructural evolution of the passivating film.In this study, we observe that the polycrystalline aluminum film locally corrodes in the area irradiated by the electron beam, depending upon both the irradiating electron current density and the concentration of chloride in the electrolyte. We investigate how different potential radiolysis mechanisms may contribute to this effect, including: radiolysis of the liquid leading to pH change, interaction of the secondary electrons at the liquid-passive film interface, and break-down of bonds in the passive oxy-hydroxide layer which protects the aluminum surface from uniform attack.We observe that aluminum samples do not undergo this preferential corrosion in the absence of the chloride-containing electrolyte, however, the beam-irradiated area will preferentially corrode even if the electrolyte is introduced after the irradiation has ceased. We have also observed for samples with a thicker alumina film (grown by atomic layer deposition) that the amorphous alumina film would crystalize for sufficient dose of electrons; it is expected that this crystallization accompanies voiding as the film densifies as described in a study by Nakamura, et al.1. Finally, in a third experiment where a square trench was milled out of the deposited aluminum by focused ion beam we observed that the edge of the square, covered in passive oxide, was not attacked randomly but receded in all directions upon irradiation. These experiments suggest that the electron beam interacts primarily with the oxide film, where structural changes may permit intrusion of the aggressive chloride, leading to corrosion.In summary, this work seeks to explain an observed pitting initiation mechanism developed under electron irradiation, and thereby allow enhanced understanding of localized corrosion mechanisms. We acknowledge NSF for funding this research (DMR-1309509) and use of the Micro and Nanoscale Fabrication Clean Room and the Nanoscale Characterization Core within the Center for Materials, Devices, and Integrated Systems at RPI. In particular we thank Ray Dove, and Deniz Rende for technical assistance on the instruments used in this study, and Brent Engler for assistance with sample preparation.[1] R. Nakamura, M. Ishimaru, H. Yasuda and H. Nakajima, J. Appl. Phys. 113, 064312 (2013).

Functional properties of multicomponent nanomaterials, such as multimetallic, mixed oxide, or supported nanocatalysts, depend on their size, composition, and particle morphology. Due to their nanoscale size, properties and performance of multicomponent nanomaterials in their functional application is critically linked to underlying nucleation mechanisms. While classical nucleation theory is oft-applied as a framework to interpret nucleation, there is no theoretical basis for its application to multicomponent nanomaterials, especially those synthesized directly onto nano- and mesostructured supports with unknown numbers and types of heterogenous nucleation sites. In this talk, we will describe a liquid cell electron microscopy approach to investigate heterogeneous nucleation mechanisms using novel radiolytic synthesis routes and quantitative and statistically sound nucleation measurements. Notably, we employ radical scavengers to prevent oxidative back reactions during electron beam induced nucleation and growth of single and multimetallic nanostructures. Through experiment and kinetic simulations we find that the efficacy of scavengers depends on electron dose rate. We measured nucleation kinetics using novel survival functions traditionally employed in macroscale nucleation experiments, which suggest heterogeneous nucleation occurs on membrane surface sites having a broad distribution of activation energies.

Covalent organic frameworks (COFs) are crystalline, highly nanoporous materials, consisting of extended periodic ligand network nanostructures, which are extremely amenable to synthetic design by appropriately selecting the monomers used in synthesis. Though progress had been made in the development of novel COFs, largely by trial and error approaches, little is understood about the fundamental nucleation/growth mechanisms that lead to formation of the different COF nanostructures and morphologies, greatly limiting our ability to rationally develop next-generation COF materials.Advances in liquid-cell transmission electron microscopy (LCTEM) instrumentation now enable direct variable-temperature (VT)-LCTEM observations of fully hydrated/solvated systems while uniformly heating the liquid. Here, we study the nanoscale nucleation and growth during the formation of COF-5 nanoparticles (NPs) using VT-LCTEM. The Dichtel lab has developed a new COF-5 synthesis route for producing size-stabilized NPs (diameters 20-200 nm), whereby the diameter of the population of discrete colloidal COF-5 NPs can be readily modulated by tuning the relative solvent concentrations in the precursor solution. In our VT-LCTEM studies, COF nucleation/growth does not occur at room temperature, even when irradiated by the e- beam at low dose rates. However, when the same COF-5 growth precursor solution is heated to, and held at 80 deg. C, discrete COF NPs nucleation and growth, seeded on the SiNx window surface, is observed (Figure 1A), which could be consistently reproduced in multiple separate VT-LCTEM experiments. We employ the MOTA-method for particle tracking and quantitative size-measurement image analysis to accurately determine the particle size of the population as the particles grow and size-stabilize over time (Figure 1B). We use these quantitative VT-LCTEM measurements as both a complementary characterization tool to bulk-scattering techniques for accurately determining the true size and morphology of nanomaterials in solution, and more importantly as a window into the underlying mechanisms of thermally-triggered COF formation, with the aim of applying this knowledge to intelligently modify synthesis conditions to promote the formation of more desirable COFs.

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3:30 PM - *TC02.02.06

In Situ TEM Revealing of the Fundamental Physical and Chemical Process of Both Energy Storage and Nanoparticle System

The fading and eventual failure of energy device is closely related to the structural, chemical, and electronic evolution of the active materials in the device. However, detailed characterization of these evolutions during the device operation has been a significant challenge, requiring innovative technique development and creative experiments. In-situ transmission electron microscopy and spectroscopy, coupled with other in-situ spectrometry, appears, no doubt, to be the essential approaches that enable the capturing of these evolutions with high spatial and fast temporal resolution. In this presentation, I will highlight recent progress on in-situ and operando S/TEM imaging and spectroscopy techniques and their application for probing the fading mechanism of rechargeable batteries and the deactivation of catalyst in proton exchange membrane (PEM) fuel cells. For rechargeable battery, in-situ high resolution imaging enables direct observation of structural evolution, phase transformation and their correlation with mass, charge and electron transport, providing insights as how active materials failure during the cyclic charging and discharging of a battery. For the PEM fuel cell, direct atomic level visualization lead to the isolation of the critical factors that contribute to the deactivation the catalyst involving H2, O2, and H2O. At the same time, I will highlight recent work on direct in-situ TEM measurement of interaction of nanoparticle under liquid media. In perspective, challenges and possible new direction for future development will also be discussed. In essence, integration of different analytical tools was viewed as the key for capturing complementary information.

Tremendous efforts have been devoted to enhancing the oxygen reduction ORR properties of Pt-based nanoparticles through size- and morphology- controlled synthesis.1 Recently, the core-shell catalysts with atomic layered surface Pt through liquid phase atomic layer deposition has been proven to be one of the most promising ORR catalysts with high activity and low consume of Pt.2-5 However, corrosion is a major and unavoidable challenge for the degradation of properties of catalysts during electrocatalysis, which restricts the practical application of catalysts severely.6-7 Therefore, it has been an urgent issue to understand the evolution and mechanism of both atomic layer formation and corrosion of Pt based atomic layered core-shell catalysts during the reaction with an aim to the effective utilization of the catalysts. 8In this presentation, we will first report a new 3D growth mechansim for the formation of core−shell nanostructures involving a hybrid process with: initial island growth, surface diffusion, and subsequent layer growth. The apparent layer-by-layer growth is a dynamic process by balancing both island deposition and surface diffusion.9 Secondly, the in situ study of corrosion behavoir of Pt based atomic layer core-shell catalysts will be carried out via liquid phase in situ TEM technique to demonstrate the direct relationship between the dynamical evolution of structures and compositions of ORR catalysts.10 This in situ study of hybrid growth and corrsion mechanism of Pt based atomic layered core-shell catalysts provide valuable insight and fundamental understanding to design highly acitve and durable electrocatalysts.

The development of nanotechnology, particularly of nanoparticles, is having a revolutionary effect in science and technology. Nanoparticles are defined as materials with more than 50% in the number size distribution, that size range from 1-100 nm by the European Commission. And they are contributing to the reduction of uncertainties about the potential impact of nanomaterials on health and the environment. Therefore particle size and particle size distribution are very critically important parameters.In recent years, toxicity assessment method using nanoparticle in stable suspension has been emphasized in safety evaluation of nanomaterials. The nanoparticles dispersed in the aqueous solution have the possibility of creating an artifact that does not reflect the state of the dispersion aqueous solution. Because there are trapped multiple particles during the vaporization process depending on the size of the droplet. However, these considerations have only been reported by theoretical calculations. Confirmation of the conditions for measuring the size and size distribution reflecting the state of the dispersion aqueous solution is fundamental to reliable nanomaterial characterization.In this work, the size and size distributions of liquid suspension containing well-dispersed standard nanoparticles are measured by scanning mobility particle sizer (SMPS). At this time, we realized that the estimation based on the simple theoretical calculations and the error factors of measurement does not properly reflect the actual situation. First, we calculated the water droplet size of electrospray using SMPS system include differential mobility analyzer (DMA). The spraying was performed using a known concentration of aqueous sucrose solution prepared by dissolving sucrose into DI water. The residue particle size can be controlled by the sucrose concentration. The droplet size is assumed to be related to the sucrose residue diameter. From this study, we can know that contains some of the nanoparticles in one droplet. Second, the size distribution measurements of aerosolized particles are made using variety certified reference materials (CRM). These were compared with certificate values. And we have found reliable measurement conditions through repeated measurement. As a result, this measurement was found suitable for use as a particle number concentration standard in calibration of particle counting instruments in the particle size range for < 100 nm. In addition, we measured reference materials of mixed with different concentration ratios.

Recently, upconversion nanocrystals have been intensively studied for a range of applications including bio-imaging, bio-sensing, solar cell, photocatalysis, and laser cooling. Among the upconversion nanocrystals, sodium-yttrium-fluoride (NaYF4) is the best host material which shows high quantum efficiency and good biocompatibility. A low-cost, scalable, reproducible hydrothermal approach can be applied to achieve different sizes, morphologies, and phases of NaYF4 nanocrystals. This talk will discuss NaYF4 nanocrystals formation processes and mechanisms with in-situ transmission electron microscopy (TEM). The reagent precursors in the mixture of oil, water, alcohol, and surfactant characterized with the cryo-TEM show the initial formation of the microemulsion. In-situ liquid cell TEM experiments show a series formation processes, including microemulsion droplets’ movement and mass transfer, nanocrystals nucleation, aggregation, and attachment. ‘In-situ’ optical trapping experiments have been applied to investigate real-time cation-exchange at the nanocrystal-solid/liquid interface. Synchrotron X-ray absorption has also been used to characterize the rare-earth-ion-dopants’ oxidation states and the carbon impurity in NaYF4 nanocrystals, which can help the understanding of upconversion efficiency and background absorption.

4:45 PM - TC02.02.10

In Situ Study of the Controlled Growth of Electron Beam-Induced Branch-Shaped Au Particles

Understanding the nucleation and growth of colloidal crystals provides fundamental guidelines in materials science. In particular, unveiling the mechanisms of crystal growth is key to the shape control of metallic crystals which possess similar surface free energies and chemistry.[1] Herein, we exploit in situ transmission electron microscopy in liquid to control and study the growth of gold (Au) particles by radiolysis. Varying the liquid layer thickness while maintaining a constant electron dose rate and Au ion supply produces Au crystals with different habits, from spheres, rods, and prisms to branched particles. We propose that a high concentration of hydrated electrons [eh −] induces diffusion limited growth into branched particles, while a lower [eh −] promotes the development into spheres, rods and prisms. In addition, we show the growth of Au particles can be regulated by a strong Au-binding amyloid (i.e. islet amyloid polypeptide).[2] Spherical Au particles (~50-100 nm) grow on the amyloid fibril aggregates while large Au branched particles (~2 μm) form in the absence of the fibrils.

Direct ethanol fuel cell (DEFC) is an important sustainable energy vector, but its development is impeded by lacking active and robust anode catalysts. We report here new findings of an experimental-theoretical investigation of composition-tunable carbon-supported platinum-ruthenium (PtRu/C) nanoalloy catalysts for ethanol oxidation reaction (EOR), the anode reaction of DEFC. Our study focuses on elucidating the relationship among the bimetallic composition, atomic structure and catalytic activity of the catalysts in EOR. The composition and structural evolution of the catalysts in EOR were probed by ex-situ and in-situ synchrotron high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis and in-situ energy dispersive X-ray (EDX) analysis. The results show that the activity for EOR reaches the maximum at an atomic Pt: Ru ratio of 1:1. In the EOR process, the catalytic activity is shown to be improved significantly, which can be attributed to the atomic scale structure changes of the nanocatalysts, as revealed by in-situ HE-XRD/PDF/EDX data. Using nanocluster models for the PtRu nanoalloys, density functional theory study revealed that the highest adsorption energy of ethanol and the shortest Ru-O bond distance at an atomic Pt: Ru ratio of 1:1, which coincides with the experimental finding. These findings have significant implications for the design and synthesis of active anode catalysts for DEFCs.

The functionality of lithium ion batteries is dependent upon the redox phase transformations that occur between charge and discharge. Monitoring the mechanism of a cathode material's transformation is crucial to understanding intrinsic properties directly impacting device performance. Probing these materials over a range of length scales is necessary to fully describe the system; one such is the single particle. In situ and operando measurements are preferable as they allow for the direct observation of dynamic conditions within the cell. We have thus leveraged an x-ray microprobe to perform operando diffraction mapping of micrometric secondary particles relevant to current battery technology. The spatial resolution afforded by this technique permits us to resolve the diffraction patterns collected over each individual particle from those of neighboring particles. LiNi0.80Co0.15Al0.05O2, one member of the so-called layered oxide family of cathode materials, has a transition metal ratio that balances capacity, reversibility, and structural stability. These materials are intriguing to study, on account of their high theoretical capacities. However, only ~50% of that capacity is practically achieved. Closing this gap would dramatically increase energy storage density of the material. Here we demonstrate the technique development and observation of how the redox reaction propagates through the single secondary particle, identifying chemical phases as a function of electrochemical potential.

8:00 PM - TC02.03.03

Comparison of the Growth of Metallic Silver Filaments in Ag2WO4 Samples by Means of Electron Beam and Ultraviolet Irradiation

In recent years, silver-based ceramic oxides have been widely investigated by the scientific community because of their unique bactericide, fungicide, photocatalytic and optical properties [1]. In particular, the nucleation and growth of metallic silver have been commonly detected on the particle surfaces of these materials, when exposed to an electron beam [2]. Therefore, this phenomenon is able to affect the structural and morphological features of these oxides, modifying the behavior of their physicochemical properties. Having seen the impact of those researches, the main aim of our study was to investigate the growth process of metallic silver filaments in silver tungstate (Ag2WO4) by using two different mechanisms, i.e., electron beam and ultraviolet irradiations. This tungstate was synthesized by the chemical precipitation method, involving the rapid injection of precursor ions (Ag2+ and WO42-) into a dimethyl sulfoxide solution heated at 120 °C. Rietveld refinements indicated all as-prepared samples crystallize in an orthorhombic structure with space group (Pn2n). No secondary phases were identified in these diffractograms. Scanning Electron Microscopy (SEM) images showed that the Ag2WO4 samples are composed of several rectangular rod-like microparticles. When they are exposed to electron radiation on a Transmission Electron Microscope (TEM), an in situ growth of Ag filaments was detected, especially on the ends of these rods. The high electronic charge concentration in those regions, by the exposure to the electron beam under high vacuum, promotes the growth in a preferential way by the migration of silver atoms. It was more pronounced and faster when the current density of the electron beam was gradually increased. After reaching a final equilibrium condition, the indexing of electron diffraction patterns revealed the presence of metallic Ag particles found on the filaments as well as some crystalline tungsten dioxide (WO2) regions with monoclinic structure. This information implies in a complex morphological change of these microparticles by the electron beam. In this case, the spontaneous migration of silver atoms resulted in an amorphization process of Ag2WO4 rods followed by a local recrystallization of WO2 nanoparticles. On the other hand, when subject to ultraviolet irradiation, there is the formation of several irregular Ag filaments on all surfaces of these rods. Thus, the distribution of Ag surface sites in Ag2WO4 rods actuated as preferred growth points for the migration of Ag atoms from bulk to surface. These morphological features remained very stable, even with the action of the electron beam during later TEM. The growth of metallic Ag in Ag2WO4 induced by electrons and ultraviolet wavelengths have a completely distinct nature.

Electrospinning has been studied as a facile and useful method to fabricate nanofibers from a polymeric solution and nanofiber-based structures were introduced in a variety of fields including membranes, filters, biological scaffolds. However, the properties of nanofibers could be extremly different from those of bulk due to the size effect. It is important for developing useful applications with nanofibers to understand size-dependent change in properties such as a glass transition temperature.In this study, the glass transition temperature of thin polyvinyl acetate fibers were measured as a function of fiber diameter. The polymer fibers with various diameters were prepared using electrospinning method by controlling the concentration of polymeric solution. Each nanofiber was mounted on a quartz tuning fork (QTF), which is a piezoelectric resonator with two prongs, as a bridge. The viscoelastic property of mounted fiber was obtained from the resonance frequency and the qulity factor of the QTF. It is found that the glass transition decreases in temperature as the fiber diameter is reduced.

An α+β type titanium alloy was subjected to various periods of recrystallization annealing and the resulting microstructural evolution was characterized. It was found that the recrystallization rate of the β phase was higher than that of the α phase, owing to the high strain energy storage of this phase during large deformation forging, and the recrystallized fraction of both the α and β phases increased with the increasing holding time at 740 °C. The recrystallization fraction of the β phase accounted for 70.13% after annealing for 5h. However, the average grain size remained unchanged when the recrystallization fraction reached approximately 54%, indicating that high recrystallization degree restrained the nucleation of recrystallization. Furthermore, the spatial microstructure which consisted of a globular, homogeneous, and equiaxed α phase dispersed in sub-structured β matrix grains, was characterized via a novel three-dimensional electron backscatter diffraction technique. The grain orientation and morphological parameters, including the equivalent-sphere diameter and number of neighboring grains, were calculated and discussed.

MEMS based devices have significantly improved our capability to capture the dynamic behavior of material inside the TEM at elevated temperatures and high spatial resolutions. The superior thermal stability of these MEMS based heating holders enables us to study a wide range of material systems ranging from nanoparticulate to bulk samples. In situ investigations on nanoparticulate systems are relatively straightforward, but the study of bulk material systems is challenging due to complications in the preparation and the transfer of these specimens onto the MEMS chip. Previously, TEM specimens from bulk materials were prepared either by FIB milling an electron transparent fragment from an electro-polished foil or by thinning a thicker lamella placed across the window of the MEMS chip with an ion beam. In the former case, the site selectivity is limited to features from electron transparent regions of the electropolished foils, and the specimen is not mechanically robust so it can be damaged easily during the transfer onto the MEMS device. In the latter case, there are challenges in transferring the specimen onto the MEMS device, and the ion beam can damage the specimen and/or device during final thinning.Here, we describe a novel specimen preparation protocol for the preparation and transfer of specimens from bulk samples onto a MEMS chip. In our work, we use an FEI Helios Nanolab 460F1 FIB and an FEI NanoEx-i/v heating holder, but the approach can be adapted readily for other FIBs and heating holders. This approach utilizes a specimen geometry with a thick layer surrounding the electron transparent region and a planar lower surface, which increase the mechanical stiffness, the area of the electron transparent region, and the contact area between the specimen and the micro-heater surface on the MEMS chip. The method involves a stage block with a flat top surface for mounting the bulk sample, and an inclined surface facing away from the ion beam for the MEMS chip. This arrangement minimizes the ion beam flux on the MEMS chip during milling. The stage block allows the use of conventional FIB lift out and milling procedures to prepare the specimen from the bulk sample. The specimen is then transferred to the MEMS chip by tilting the bulk stage to allow for the accurate and reliable placement of the specimen across the MEMS window by imaging simultaneously using the electron and ion beam. Data from heating experiments on cross-sectional specimens obtained from various bulk metallic samples are presented to demonstrate the quality of the specimens that can be prepared using this approach.

8:00 PM - TC02.03.07

Probing Local Structural Changes Using In Situ Indentation and Raman Spectroscopy

Understanding materials response or structural transformations at elevated pressure are essential in developing new electronic or structural materials. Combined scanning probe microscopy and instrumented indentation technique become popular among materials scientists to study the mechanical behavior of small length scale materials. A unique experimental configuration was adopted, where instrumented nanoindentation was integrated with Raman spectroscopy to probe local stress induced structural changes. Such an in-situ indentation-Raman instrument has immense potential to study pressure-induced phase transformation and solid-state reactions in pharmaceutical materials and further to establish structure-property relationships. We have rationalized the non-uniform structural modifications during bending state of the highly flexible halogenated N-benzylideneanilines organic crystals. Foremost, the indentation technique was utilized for three-point bending tests on the crystal and later on the in-situ Raman spectroscopy identified the structural perturbations details in the different region of the bent state of elastic crystals. The capabilities of the instrument were further demonstrated by performing indentation and Raman studies on monocrystalline silicon and anti-inflammatory drug β-piroxicam.

8:00 PM - TC02.03.08

Elastic Properties of an Epoxy Resin Polymer During Structural Reconstitution

In this study, the cure kinetics of the two-component epoxy-based polymer DGEBA/DETA is investigated using concurrent Raman and Brillouin light scattering. Raman scattering allows one to monitor the in-situ reaction and quantitatively assess the degree of cure, while the Brillouin scattering measurements yield the elastic properties of the material, which provides a measure of the network connectivity. We show that the adiabatic modulus of the polymer evolves non-uniquely as a function of cure degree, depending on the cure temperature and the molar ratio of the epoxy system.Accordingly, two mechanisms contribute to the increase in the elastic modulus of the material during curing. First, there is the formation of covalent bonds in the network during the curing process. Second, once the bonds are formed, the structure undergoes structural relaxation toward an optimally packed configuration of the network, which enhances non-bonding interactions. Both contributions are apparent in the adiabatic modulus derived from Brillouin scattering, as it reflects the elastic response of the polymer network in thermodynamic equilibrium. To further ascertain the notion of structural reconstitution affecting only non-bonding interactions, we subject the epoxy to various degrees of strain using a miniature tensile tester mounted in the beam path of the light scattering setup, and simultaneously measure the adiabatic and isothermal elastic moduli as a function of the applied strain and deformation rate. Our analysis reveals to what extent the contribution of non-bonding interactions to structural rigidity in cross-linked polymers is reversible, and to what extent it corresponds to the difference between adiabatic and isothermal moduli, i.e., the so-called relaxational modulus.

8:00 PM - TC02.03.09

High-Resolution X-Ray Computed Tomography and Direct Numerical Simulation for the Measurement and Calculation of Decreased Permeability in the Wall-Flow Diesel Particulate Filter due to the Accumulation of Lubricant-Derived Ash

Catalytic diesel engine exhaust aftertreatment components, especially the diesel particulate filter, are subject to degradation due to various reasons over normal component lifetimes. One form of degradation in the catalytic diesel particulate filter (cDPF) is the significant rise in pressure drop due to the accumulation of engine lubricant-derived ash (inorganic, incombustible ionic crystalline solids consisting of Ca, Mg, Zn, S, P and O) which coats the inlet channel walls effectively decreasing the permeability of the wall-flow component architecture. This form of catalyst degradation has been found to reduce vehicle fuel economy by as much as 5%. High-resolution X-ray Computed Tomography (CT) with a transmission X-ray source (voxel size ~600nm) has been used in combination with direct numerical simulation techniques to calculate the permeability and pore structure changes of the combined ash-catalyst substrate system to better understand the effects of ash accumulation on engine aftertreatment component functionality. The current CT resolution allows direct and accurate 3D visualization of the catalyst substrate structure, the individual ash particles (which have an average size of 1-2µm) and the ash which penetrates into the substrate surface pores. This study will discuss the sample preparations necessary for such high CT resolution, the combination of CT and direct numerical simulation (CT dataset segmentation and flow simulations), the comparison between calculated and experimentally measured permeability values and the implications of the ability to calculate permeability in the combined ash-catalyst substrate system.

In-situ SEM mechanical tests are key to study crystal plasticity. In particular, imaging and diffraction (EBSD) allow to have access to microstructure and surface kinematics all along the mechanical test. However, to get a full benefit of the different modalities, it is necessary to register all images and crystallographic orientation maps from EBSD into the same frame. Different correlative approaches tracking either Pt surface markings, crystal orientation or grain boundaries, allow such registrations to be performed and displacement as well as rotation fields to be measured, a primary information for crystal plasticity identification. However, the different contrasts that are captured in different modalities and unavoidable stage motions also give rise to artifacts that are to be corrected to register the different information onto the same material points. The same image correlation tools reveal very powerful to correct such artifacts. Illustrated by an in-situ uniaxial tensile test performed on a bainitic-ferritic steel sample, recent advances in image correlation techniques are reviewed and shown to provide a comprehensive picture of local strain and rotation maps.

Most one-dimensional nanostructures are grown by a vaporous or an aqueous method. However, both of the methods have some disadvantages: vapor-phase growth processes of high costs are typically carried out at high temperatures, with the release of pollutant by-products, while aqueous processes need specific expensive pollutant precursors. Recently, we proposed a BHR (bond breaking-hydrolysis-reconstruction) mechanism for stress-induced spontaneous growth of one-dimensional oxide nanocrystals on oxide bulks or films in an ambient atmosphere at room temperature. In this study, we further systematically grew ZnO, TiO2, ZrO2 and SiO2 nanocrystals, and investigated the activation energies (thermodynamics) and rates (kinetics) of the early-stage nucleation and late-stage growth of the nanocrystals. An in-situ transmission electron microscopic (TEM) observation of oxide (quartz) nanocrystal growth from mechanically broken granite was conducted in an ambient cell (liquid cell filled with only air and moisture) to investigate the stress-induced spontaneous growth process. The in-situ TEM observation indicated that the dangling surface of the broken granite would first hydrolyze to form hydrate islands. In lack of moisture or under exposure to electron beam, the hydrates decomposed to form stable oxides. A cyclic hydrolysis-dehydration process then yielded the growth of the nanocrystals. Thermodynamics and kinetics studies reveal that the nucleation/growth of the oxide nanocrystals follows [log ΔL = log k + n log t] where the rate constant k depends on the activation energy of nucleation and the time exponent n depends on the activation energy of growth. The activation energies of nucleation (ZnO < TiO2 ~ ZrO2 < SiO2) well consist with the measured nucleation rates (ZnO > TiO2 ~ ZrO2 > SiO2), and the activation energies of growth (ZnO ~ SiO2 < TiO2 ~ ZrO2) also accords with the growth rates (ZnO ~ SiO2 > TiO2 ~ ZrO2).

8:45 AM - TC02.04.02

In Situ Observation of the Surface of Working Gold Electrodes by Environmental TEM

Gold has a wide range of important applications for nanoscale characterization and sensing technology in chemistry and bioscience. As is well known, gold surfaces play a role in gas conversion as catalysts [1]. However, there have been much less experiments at the atomic scale on the gold surfaces under electrostatic potential. Here, we investigated the surface of a gold electrode under electrostatic potential and in gas environments using high spatial and temporal resolution environmental transmission electron microscopy (ETEM).ETEM observation was carried out at the various magnitude of electrostatic potential and in various gases. In vacuum, facets appeared clearly on the crystalline gold surface. In contrast, the gold surface in gases became rough via the surface migration of gold atoms. Though the dynamic phenomenon was affected partially by electron beam irradiation, we could clarify the intrinsic nature of surface disordering in the working gold electrodes. We have succeeded in capturing the extraordinary atomic phenomena at high spatial and temporal resolution. We will show in-situ ETEM movies in different environments to contribute to the further advancement of materials science on surfaces.

The environment, such as temperature, pressure and atmosphere, has a significant impact on the solid surfaces, which may result in structural and electronic changes including gas adsorption, electron transfer and stress variation, making it challenging to accurately interpret the physical and chemical properties of surfaces. To address such an important issue, we introduce the environment into transmission electron microscope, which is supposed to work in high vacuum, to study the structural evolution and its impact on the physicochemical properties of solid surfaces at the atomic scale under gas environment and provide valuable information for designing and synthesizing high-performance materials.In this report, firstly I will introduce the in-situ observation of surface reconstruction of TiO2 induced by heating under oxygen. The oxygen prevents the surfaces from the irradiation of electron beam, making it possible to first observe the real-time surface reconstruction at atomic resolution during the experiments. Meanwhile, the in-situ data of the stress variation of the surface during the reconstruction was acquired, which directly verified the theoretical work of stress driven reconstruction published 15 years ago. [Nano Lett. 16 (2016) 132-137]Then we will present our recent in-situ study on the catalyst nanoparticles under high temperature and atmospheric pressure (105 Pa) using gas-cell system in TEM. The atomic resolution TEM images at 600K under 1 bar hydrogen pressure demonstrate that the environment has a huge impact on the morphology of the PdCu nanoparticles, and considering the temperature and gas pressure, a decent model was proposed, which can well explain why the PdCu nanoparticles change their morphology under deferent environment. [Angew. Chem. Int. Ed. 55 (2016) 12427-12430]

9:30 AM - TC02.04.04

Understanding the Effects of Shape and Surface Faceting in the Hydrogenation Kinetics of Palladium Nanoparticles

Nanoparticles have become increasingly attractive platforms for chemical conversion, including catalysis, ion intercalation, and phase transformations. Their high surface-area-to-volume ratio and tunable shape and size enable improved performance over bulk samples. Their surface faceting is also thought to impact chemical conversion thermodynamics and kinetics, though visualizing the role of surface termination on such reactions in-situ and in real time remains an outstanding challenge. Here, we investigate the role of nanoparticle surface faceting by visualizing the hydrogenation of individual palladium nanoparticles with 2nm spatial resolution and 0.5s time resolution. Using a suite of techniques in an environmental scanning transmission electron microscope (TEM), we directly observe the hydrogen-intercalation-driven phase transformation and compare the behavior in two single-crystalline Pd nanoparticles: octahedral nanoparticles with {111} terminated surfaces and cubic nanoparticles with {100} terminated surfaces. We first collodially synthesize octahedral and cubic nanoparticles with sizes ranging from 50nm to 100nm and then use electron diffraction to verify that in equilibrium, Pd octahedral and cubic nanoparticles do not exhibit phase co-existence, similar to other single-crystalline shapes. Then, we use scanning TEM, dark-field imaging and electron energy loss spectroscopy (EELS) to visualize the hydrogenation kinetics and find that both octahedral and cubic nanoparticles uptake hydrogen from their corners. While cubes form a [100] phase front that propagates across the nanoparticle, octahedra can support a multitude of interface directions, including [100] and [111]. The time for the phase transition is, on average, equal for both cubes and octahedra. Moreover, the phase transformation progression has a linear dependence on time, indicating that the transformation is not diffusion limited, and suggesting that the hydrogenation reaction is limited by either hydrogen splitting at the surface or the lattice rearrangements needed for the phase to propagate across the particle. Our results highlight the role of shape in chemical transformations and will help inform more rational design of nanoscale catalytic and energy storage materials.

Localized surface plasmon resonances (LSPRs) are generated in certain metal nanoparticles due to the interaction of photons or electrons with the metal’s free electrons. Recently, optical methods have been used to show that ‘hot electrons’ generated from the decay of surface plasmons can trigger chemical reactions at room temperature [1-2]. Understanding the reactions promoted by LSPR is important for designing efficient catalytic systems for a wide range of energy and environmental applications. However, many important questions related to such reaction processes remain unanswered due to the complexity of the reaction kinetics, and the limited spatial resolution of current optical methods. One of the fundamental questions remain unanswered is how the nanoscale changes in the particle morphology and/or the dielectric environment during photocatalytic reactions affect the spatial distribution of LSPR profiles and if that can be correlated with the location of each reaction step.We use an ensemble of techniques to characterize various aspects of LSPR-promoted chemical reactions in an environmental transmission electron microscope equipped with a monochromated electron source, which yields an energy resolution of 80 meV. In particular, we focus on the LSPR-promoted dissociation of H2 gas near aluminum nanoparticles, and the resulting formation of AlH3 at room temperature. Electron energy-loss spectra (EELS) imaging, with different energy dispersions, is used to acquire both elemental and LSPR maps from the same particle. These combined spectrum images allow correlation of the LSPR profile and the morphology of different composition in the nanoparticle, providing insight into particle engineering for optimum LSPR output. The result shows that the LSPR intensity distribution is determined by the shape of the Al core, while the LSPR energy distribution depends on the local Al2O3 shell thickness. Comparison of LSPR locations and shifts between the EELS maps, before and after a 100 Pa H2 gas exposure, show the effect of the gaseous environment on the LSPR generated on the nanoparticle surface, revealing selective gas adsorption sites. Atomic-resolution movies and time-resolved EELS are acquired to monitor the crystallographic transformation and chemical changes in the particle, confirming the metal hydride formation due to the LSPR promoted reaction. This combined approach offers time-resolved, atomic-scale information on the dynamics of LSPR-promoted reactions, providing insights into how to engineer nanoparticles with higher photocatalytic efficiency [3].

[1] Sil, Devika, et al. ACS Nano 8(8) (2014), 7755-7762.[2] Zhou, Linan, et al. Nano Lett. 16(2) (2016), 1478-1484.[3] The authors acknowledge funding from the Cooperative Research agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, Award 70NANB14H209, through the University of Maryland.

The excellent spatial and temporal resolution available in ETEM is useful in exploring the dynamic phenomena that underpin crystal growth, catalytic processes or nanoscale phase changes. Here we examine crystal nucleation, growth and epitaxy on suspended graphene using what could be called “multi-modal ETEM”. We deposit Au nanocrystals on graphene then heat and flow chemical vapor deposition precursor gases such as disilane and digermane in situ to achieve catalytic epitaxial growth of the semiconductors on graphene. Aberration corrected images and diffraction provides details of the graphene structure and semiconductor epitaxy while dark-field techniques yield crystal orientation relationships and defects. Ultra high vacuum TEM, in particular using an integrated side chamber with evaporation capabilities, allows us to control substrate cleaning and carry out growth without side reactions such as oxidation to evaluate the effects of surface contamination on growth. Imaging at low accelerating voltage or with low dose techniques helps show the extent to which beam-induced damage affects nucleation. The combination of information from these different types of ETEM experiment allows us to relate epitaxy to the nucleation environment of the semiconductor, with the presence of a solid catalyst, a liquid catalyst or with no catalyst present. We suggest that in general going beyond a single imaging mode or type of gas environment enhances the power of ETEM to extract growth physics during materials transformations.

The ability to monitor dynamic processes in-situ is crucial for understanding structure-property relationships in nano-engineered materials. In the past decade, the majority of atomic-scale electron microscopy studies involving gas-solid interactions were conducted in an environmental transmission electron microscope (ETEM), where the gas pressure is typically limited to no more than 1/100 of atmosphere. Recently, it has become possible to overcome this limitation through the use of a MEMS-based, electron-transparent windowed gas cell. In this talk, we illustrate the capability of this device as applied to our study of two important catalyst systems: (1) the CO-induced Pt nanoparticle (NP) surface reconstruction at saturation coverage (2) the ordering and Pt surface enrichment in supported Pt3Co NPs.Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Here, we characterize atomic-scale details associated with the structural rearrangement of supported Pt NP surfaces induced by the adsorption of CO at saturation coverage and elevated temperature. It was observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet-specific reconstruction due to CO adsorption, where flat {100} facets roughen into vicinal stepped high Miller index facets, while flat {111} facets remain intact. The in-situ electron microscopy evidence shows excellent agreement with the result of density functional theory (DFT)-based calculation and in-situ infrared spectroscopy, providing a clear insight for CO-induced reconstruction of (100) sites.Another example is the in-situ observation of Pt shell formation in Pt-metal (Pt-M) catalysts. The core-shell structured NP, having a thin Pt shell on the bimetallic Pt-M (M: Fe, Co, Ni, etc.) core, is a promising oxygen reduction reaction (ORR) catalyst in polymer electrolyte membrane fuel cells. To better understand the formation process of the Pt shell, which is crucial for enhancing ORR activity, we performed in-situ TEM experiment on carbon-supported Pt3Co catalysts, combined with first principle calculations. The initial disordered Pt3Co NPs were found to transform to an ordered intermetallic phase after high temperature (720 °C) annealing in 760 Torr of O2, then followed by layer-by-layer Pt shell growth on (100) surfaces via Ostwald ripening at low temperature (300 °C). This novel oxygen-driven core-shell formation may thus pave a way for designing and tailoring the structure and performance of Pt-Co ORR catalyst.

Electron energy loss spectroscopy has been used to study the changes in materials during in-situ TEM experiments since the early days of in-situ TEM. EELS spectra can map the redistribution of elements in a material nanostructure, monitor oxidation or reduction, or even observe the exchange of elements from the gaseous or liquid environment into solid structures during growth processes.In the past EELS spectra or maps were usually taken before and after some observed or expected transformation. Spectra were typically not acquired throughout the course of these transformations for a variety of reasons, including beam damage, sample instability/drift, and because the acquisition of EELS spectra/maps was too slow for continuous monitoring.Today, using sensitive new direct detection cameras like Gatan’s K2 to collect the EELS signals, lower dose rates can be used to reduce beam damage, and spectra can be acquired rapidly while maintaining reasonable signal-to-noise in the acquired spectra. New MEMS-based sample holders now significantly reduce the drift previously associated with heating materials in the TEM. Due to these advances, it is now possible to continuously collect EELS data, producing the equivalent of a video during in-situ transformations. Data acquired using several methods will be shown, including counted EFTEM videos, time-sequences of EELS spectra, and time series of EELS maps.

Many electronic devices, such as field-effect transistors, depend on achieving precise control of both the composition and atomic arrangement within a semiconductor nanostructure and the contact of the nanostructure with the larger-scale circuit. Control of structure and contacts involves integrating different types of materials and bridging between length scales. For example, in Si or Ge based circuits, metal silicides and germanides are commonly used in low-resistance contacts. Here we show how complex nanostructures can be formed that include silicide and germanide nanocrystals embedded within Si and Ge nanowires. We form the silicide or germanide by adding the appropriate metal to the liquid droplets of VLS grown nanowires. Solid silicide or germanide nanocrystals form in the liquid and have freedom to move and rotate until a low-energy interface with the nanowire is found. After contact is made, certain types of silicide and germanide nanocrystals remain attached to the nanowire while others break away without forming a permanent contact. Only the nanocrystals that remain attached to the nanowire can then be incorporated by continued growth of the nanowire. We have examined the factors that determine crystal adhesion to the nanowire and suggest that it depends on the symmetry of the contact interface and hence the crystal structures of the materials. This restricts the range of nanocrystal/nanowire combinations possible: for example, NiSi2 nanocrystals readily incorporate into Si nanowires because of their structural similarity, whereas NiGe nanocrystals do not attach and incorporate in Ge nanowires, presumably because of their lower symmetry. To expand the range of possible materials, we introduce the use of phase transformations within the nanocrystal. We illustrate with nanowires containing epitaxial silicide/Ge interfaces: first growing a NiGe nanocrystal on a Ge nanowire, then adding Si to transform the nanocrystal to a silicide which then attaches and is incorporated. Using in situ environmental TEM, we show the sequence of phases during the transformation and the subsequent attachment and incorporation within the nanowire. The variety of nanostructures with incorporated nanocrystals that it is possible to make using such reaction schemes potentially raises the chances for designing particular electronic and contact properties for nanostructured device applications.

For development of effective future electrochemical energy storage systems it is essential to understand the basic science associated with the gap between their theoretical energy content and their functional output. Elucidating and addressing sources of resistance is critical. As no single method can provide all the necessary information, integration of advanced characterization techniques including utilization of synchrotron light sources and electron microscopy, with advanced theory and modeling approaches, is necessary to gain new insight. This presentation will illustrate the information learned from multiscale investigations of several electrochemical energy storage materials and systems, and implications for development of future high functioning systems.

1:45 PM - TC02.05.01

The Use of Ex Situ, In Situ, and Operando X-Ray Diffraction to Understand Rate-Dependent Phenomena in Energy Storage Materials and Systems

X-ray diffraction is a powerful tool for understanding the crystal structure and phase changes of battery materials. This talk will examine how x-ray diffraction can be used to track changes in battery materials at different rates of discharge. Two oxide-based materials will be discussed as example systems.Ex-situ methods were used to study ZnFeO4, providing new evidence for an ion migration reaction. Pair Distribution Function (PDF) analysis shows no formation of an expected bimetallic phase, suggesting a previously unreported rate dependence. X-ray absorption fine structure (XAFS) was also performed, providing further verification of the XRD results.For the LiV3O8 system, in-situ and operando energy dispersive x-ray diffraction (EDXRD) reveal the structural evolution of this high-rate material. By scanning the z-axis of the battery and watching specific peaks, the locations and rates of intercalation and phase conversion reactions can be tracked while the battery is in operation. A novel cell design was also used to allow for Bragg-Brentano measurement operando. This allows for more precise refinement of the unrelaxed material. Together both datasets give quantitative information about the makeup of each phase, mapping of the phase distribution throughout the cell, and kinetic rate information.

2:00 PM - *TC02.05.02

In Situ TEM Studies of Energy Storage Mechanisms at Atomic Scales

Reza Shahbazian-Yassar 1 1 , University of Illinois at Chicago, Chicago, Illinois, United States

Electrodes in rechargeable batteries undergo complex electrochemically-driven phase transformations upon driving Li ions into their structure. Such phase transitions in turn affect the reversibility and stability of the battery. This presentation gives an overview of the PI’s research program on the analysis of electrochemical reactions at subnanometer scales. To meet this objective, we utilized in-situ transmission electron microscopy (TEM) to study nanobatteries. We show that in-situ TEM is a very powerful technique in shedding light to some of the challenges in electrochemical performance of new materials. Various anode materials including 2D materials and 1D materials (such as Phosphorene, SnO2, MnO2, ZnSb) were subjected to lithium transport studies and the transport of Li ions was visualized within their atomic structure. An important aspect of this work has been to better understand the role of defects in lithium transport studies. For SnO2 nanowires, it was observed that the Li ion transport results in local strain development preferably along (200) or (020) plans and [001] crystallographic directions. The lithiation behavior in the presence of twin boundary defects was completely different compared to pristine state with no twin boundary defect. We showed that twin boundaries in general provide a more accessible pathway for Li ion transport. Anisotropic plastic deformation was also observed along [010] directions of MnO2 nanowires.

2:30 PM - TC02.05.03

In Situ Observation of the Electrochemical Deposition of Iron in a Transmission Electron Microscope

Recently, materials science benefits largely from in-situ transmission electron microscopy (TEM) using specialized holders, which separate small reactor volumes of (the sample and surrounding) liquids or gases from the high vacuum of the microscopy column. With these novel approaches, the mechanism of dynamical process can be revealed, reaction kinetics can be quantified, and even electrochemical processes can be studied in-situ in the microscope. Here, we report on the electrochemical deposition of Fe on glassy carbon electrodes in a liquid cell. The experiments were performed on a JEM-2100 (JEOL Ltd., Tokyo, Japan) microscope operated at 200 kV which is equipped with an energy dispersive X-ray spectrometer (EDXS). A Poseidon 510 TEM (Protochips Inc., Raleigh, NC, USA) holder was used with a Gamry Reference 600 potentiostat (Gamry Instruments, Warminster, PA, USA) for conducting the electrochemical experiments (chronoamperometry). The liquid cell consists of two chips with 50 nm thin amorphous SiNx windows where the smaller one has a spacer height of 50 nm, thus controlling the total thickness of the liquid layer between the two windows. The upper, larger chip contains the glassy carbon working electrode, the Pt reference and the counter electrodes. A Fe sulphate containing solution with pH = 2 was used as electrolyte. Applying a potential of -1.2 V vs. Pt stimulates the electrodeposition of an amorphous layer of Fe, which subsequently crystallizes to Fe and FeOx, respectively. The nucleation of the crystal growth occurs instantaneously upon reaching a critical potential. The resulting deposition is discontinuous. In order to minimize artifacts such as the beam-induced radiolysis of water or secondary radical chemistry, the electron beam was blocked during the electrodeposition. The growth mechanism and the composition of the amorphous and crystalline deposits as derived from supporting EELS measurements will be discussed.

2:45 PM - TC02.05.04

In Situ Scanning Electron Microscope Observations of the Nucleation and Growth of Li Metal on Oxide Solid Electrolytes

The theoretical capacity of Li metal (3860 Ah kg–1) is much greater than those of rechargeable anodes in the present lithium-ion batteries (e.g. graphite, 372 Ah kg–1). Controlling Li plating/stripping reactions is therefore important for next-generation batteries with Li metal anodes. Inorganic-solid-state electrolytes can effectively block the growth of Li dendrites. Improved understanding of the electrochemical Li deposition/dissolution processes at Li/solid-electrolyte interfaces propels the realization of Li-S, Li-air, and all-solid-state battery.

The nucleation sites for Li metal are supposed to exist at solid/solid interfaces in SSLB. Hence, the nuclei must push either electrode or electrolyte to create their own spaces. This process is associated with generation of significant strain energies [1,2]. Previous work studied the Li plating/stripping reactions with lithium phosphorous oxynitride (LiPON) glass electrolyte layers coated with current collector (CC) films of Cu, Ni, and W [3]. These metals are unable to form alloy phases with Li. This study applies an in-situ scanning-electron microscope (SEM) observation technique to the investigation on the Li nucleation/growth and dissolution processes with Pt and Au CCs that form alloy phases with Li.

The top and bottom surfaces of a Li1+x+yAlx(Ti,Ge)2-xSiyP3-yO12(LATP) sheet (Ohara Co.) were coated with 2.5-μm-thick LiPON layers by RF magnetron sputtering. A current collector film (Pt, Au, Cu) was deposited on the top LiPON surface by pulsed laser deposition (PLD). A several-μm-thick Li film was deposited on the LiPON surface on the bottom as the counter electrode.

The voltage during the initial alloying of Pt and Au CCs with Li at 100 μA cm−2 shows positive values. After that, the voltage decreases to negative values and maintained −0.6 V to −0.8 V. These results are different from those with Cu CCs that quickly decreases the voltage from the open circuit value (OCP > 2 V) to negative values. Based on the in-situ SEM results using Pt and Au CCs, Pt and Au are alloyed with Li in the positive voltage regions. The Li nucleation occurs after the Li concentration in the CC exceeds the critical supersaturation. It is also observed that Li particles distribute with more equal interdistances with Pt and Au CCs as contrasted to the case with Cu CC. The analyzed results will be discussed.

Dynamic reaction processes that occur in battery electrodes during charge and discharge take place across length scales ranging from the atomic to the macroscale. To engineer new batteries with improved energy density, safety, and longevity, it is necessary to understand and control such processes, including phase transformations, ionic transport in materials, and interfacial degradation pathways. Here, we investigate structural and chemical transformations in sulfide materials for Li- and Na-ion batteries using a combination of in situ transmission electron microscopy (TEM) and in situ x-ray techniques (photoelectron spectroscopy and diffraction). Different metal sulfides (Cu2S, FeS2, MoS2) are synthesized as nanocrystals and thin films, and their reactions with Li and Na are probed at the nanoscale with in situ TEM. Reaction with larger alkali ions is generally thought to induce more significant structural degradation due to larger volume changes, but the results here show that for various sulfide materials, structural degradation (particle fracture, phase separation over long distances) is more dependent on the nanoscale details of the reaction process than on the magnitude of volume change induced by different alkali ions. In particular, the spatial distribution of phases after reaction is seen to be dependent on the structural similarities between the reactant and product phases, as well as the shape of the reaction front during two-phase reactions. In situ x-ray diffraction is also used to provide complementary information regarding macroscale reaction dynamics; these results often show similar macroscale changes for different alkali ions despite different nanoscale reaction pathways. Finally, in situ solid-state x-ray photoelectron spectroscopy (XPS) is shown to be effective for monitoring chemical changes at sulfide/alkali metal interfaces, and it is used to determine the effects of crystallographic orientation on interfacial transformations. Together, these results show the importance of utilizing a multi-modal approach for uncovering detailed reaction mechanisms across length scales of relevance to energy storage devices.

TC02.06: Self-Assembly

Session Chairs

Yugang Sun

Tuesday PM, November 28, 2017

Hynes, Level 2, Room 200

3:45 PM - *TC02.06.01

Peering into the Self- and Directed-Assembly of Nanoparticles

Hongyou Fan 1 2 1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , University of New Mexico, Albuquerque, New Mexico, United States

Assembly of synthetic nanoparticles enables the positioning of nanoparticles into one to three dimensional ordered arrays, facilitating integration of nanoparticle lattices into nanophotonic and nanoelectronic architectures. The functional properties of these particle materials are expected to be highly sensitive to structural factors such as coordination number, degree of long-range order, or interparticle separation distance, requiring the development of robust self- and directed-assembly pathways for precise control of structural parameters to improve optical and electronic properties of functional nanoparticles. In this presentation, I will review our past efforts in development of self-assembled nanoparticles thin film arrays and in-situ structural evolution at ambient condition. I will then extend my presentation to our recent progress in development of a new Stress-Induced Fabrication method in which we applied high pressure or stress to nanoparticle arrays to induce structural phase transition and to consolidate new nanomaterials with precisely controlled structures and tunable properties. By manipulating nanoparticle coupling through external pressure, a reversible change in their assemblies and properties can be achieved and demonstrated. In addition, over a certain threshold, the external pressure will force these nanoparticles into contact, thereby allowing the formation and consolidation of one- to three-dimensional nanostructures. Through stress induced nanoparticle assembly, materials engineering and synthesis become remarkably flexible without relying on traditional crystallization process where atoms/ions are locked in a specific crystal structure. Therefore, morphology or architecture can be readily tuned to produce desirable properties for practical applications.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Liquid crystalline nanocomposites are a novel class of self-assembling hybrid fluid nanocomposite materials, and are currently attracting significant interest from the photonics community. Such fluid nanocomposites are based on nanoparticles (carbon nanotubes, graphene, metal nanoparticles etc.) dispersed in a fluidic host material. Liquid crystallinity of the composite can be introduced either by using a conventional liquid crystal host or by the solvent-facilitated self-assembly of a liquid crystal phase for specific nanoparticle shapes, sizes and concentrations.The inherent tunability of the liquid crystal phase and the fact that nanocomposites possess a unique capability to interact with light, arising from the wide variety of properties exhibited by the usable nanoparticles, make them of significant interest for use in optoelectronics. However, in-situ spectroscopic characterisation of such fluid nanocomposite materials as they self-assemble under various applied external stimuli, e.g. electric or magnetic fields, remains challenging. In this work, we have developed theoretically, and experimentally demonstrated a practicable approach for on-chip detection of nanoparticles and the monitoring of their spatial alignment within the host fluid, using in-situ micro-Raman spectroscopy1. We have applied our technique to the monitoring of individual particles in three dimensions simultaneously. We further demonstrate the applicability of this technique beyond the monitoring of nanoparticle processes, showing potential for use in bio-monitoring of E. coli bacteria in microfluidic systems.

Focused ion beam (FIB) has emerged as a promising technology for in-situ self-assembly of three-dimensional (3D) micro- and nanostructures due to its advantages of controllable beam setup and real-time observation of the self-assembly process. These two benefits significantly increase the controllability of the physical motions of the structures with nanoscale resolution, leading to a high assembly yield. However, most of the FIB assisted self-assembly processes are based on ion induced plastic deformation in thin films, which causes significant damage in the structures due to the ion irradiation. To avoid the physical damage that could affect the performance of the 3D devices, we developed a strategy that uses the architecture of hinged-nets and programmable FIB patterning technology, which makes it possible to only expose the additional hinge material rather than the entire nanostructure. Especially, we report the first use of nanoscale polymer (PMMA) as the hinge material to generate surface tension force for nanoscale 3D self-assembly. Although the molecular density of PMMA is much lower than metal, the kinetic energy of the ions injected into the PMMA hinge induces enough thermal energy via collisions with PMMA molecules to reflow the hinge material, generating surface tension forces which transform the 2D structures into 3D micro and nano devices. Because PMMA is a light/ electron beam-sensitive material for nanoscale patterning and a relatively bio friendly material compared to metals, the polymer-based in-situ self-assembly process shows great potential for being used in the realization of nanoscale 3D biomedical devices.

Semiconductor quantum dots (QDs) and their assemblies have broad applications as optical and electrical materials in QD solar cells, photodetectors, and field effect transistors because of their quantum confinement effect. [1] In the process of device fabrication, ligand exchange is a significant step to replace the insulating alkyl ligands with small molecules and modify the surface chemistry of QDs to enhance the coupling between QDs. [2] However, the understanding of the kinetics of ligand exchange reactions on the surface of QDs is still limited. Major results in that direction would allow a more precise control of the properties of quantum dots in applied devices. In this project, we performed in situ Grazing Incidence Small-Angle X-ray Scattering (GISAXS) measurements [3] to investigate, in real-time, the ligand exchange in single component and binary quantum dot superlattices at a liquid-air interface. In particular, ligand exchanges for CdSe and PbSe QD superlattice were studied. We reveal the effect of crystal structure, particle size, ligand’s anchoring group and binding energy to the rate and yield of ligand substitution. In addition, the structural transformation of the superlattices, through the anisotropic reduction of inter-particle spacing and crystal coherence measurements, are also quantitatively characterized and analyzed during ligand exchange. In conclusion, we identified pathways to control that step of ligand exchange to successfully reduce inter-particle distances, without destroying the long-range order of the superlattices.[1] Building devices from colloidal quantum dots, Cherie R Kagan et al., Science, 2016 vol. 353 (6302)[2]The surface science of nanocrystals, Michael A Boles et al., Nat Mater, 2016 vol. 15 (141)[3]Semiconductor Nanorod Self-Assembly at the Liquid/Air Interface Studied by in Situ GISAXS and ex Situ TEM, Francesca Pietra et al., Nano Letters, 2012, vol. 12 (5515)

(Single-walled) Carbon nanotubes are infamous for their exceptional mechanical attributes, but the range of materials incorporating CNTS is presently quite limited, as the bulk properties of SWCNTs do not align with these exceptional individual properties. This shortcoming arises as the SWCNTS’ highly nonreactive surfaces encumber their dispersion into polymer matrices, simultaneuously as the high van der Waals interactions between SWCNTs make them extremely difficult to decouple. While solving these problems explicitly is beyond the scope of this study (we have no machinations towards building a space elevator), we have shown that SWCNTs are able to act as nucleating agents for crystallization in the presence of the polyetherimide ODPA-P3 (3,3’,4,4’ oxidiphthalic dianhydride and 1,4-bis[4-(4-aminophenoxy)phenoxy]bezene)---leading to a composite with promising thermomechanical properties. To our knowledge, this is the first case in which SWCNTs have induced a semicrystalline morphology within an amorphous polymer (Hegde et al, SWCNT Induced Crystallization in An Amorphous All-Aromatic Poly(ether imide), 2013).Crystallization measurements indicate radial crystalline growth b=~8.0 nm out from the central axes of the 0.6nm radius SWCNTs. Without careful consideration of the CNT dispersions’ geometry, one could assume that CNT-induced crystallization leads to a multiplication of (b/0.6)2 in the volume percent of the reinforcing phase, meaning that crystallization of the entire domain results from a loading of <1 volume % CNTs if b=8.0. However, two explanations counter this (naïve) calculation—first, the polymer assumedly becomes saturated at some amount of crystalline growth. Second, growth is impeded when the crystalline layers between multiple SWCNTs intersect at grain boundaries. Furthermore, the clustering of the SWCNTs on account of van der Waals interactions increases the frequency of these intersections. In this collaborative study between experimentalists and applied mathematicians, we study this latter geometric explanation. First, we simulate uniform CNT distributions and use an efficient geometric characterization procedure to determine which domains are occupied by crystal-CNT complexes, as a function of volume % SWCNTs. Then, we use a heuristic approach to mimic the clustering of CNTs seen in our TEM images and perform the same geometric characterization procedure. We use the random-fiber Halpin Tsai equations to predict the modulus in both cases, and compare this along with % crystallinity to experimental results.

8:00 PM - TC02.07.02

Benchmarking Equations of State from DFT across the Materials Project for Computational Discovery

Thermodynamic equations of state (EOS) for crystalline solids describe material behaviors under changes in pressure, volume, entropy and temperature; making them fundamental to scientific research in a wide range of fields including geophysics, energy storage and development of novel materials. Despite over a century of theoretical development and experimental testing of EOS for solids, there is still a lack of consensus on the most appropriate EOS under various conditions or even the metric to evaluate appropriateness. Relative root mean square deviation (RMSrD) was used as the metric for quality of fit for 8 different EOS across 85 elements and over 100 compounds that appear in literature. This metric suggests that the EOS’s described by Tait and Vinet are optimal for obtaining high quality EOS and derived properties. While chemistry and the electronic state of the material affect the RMSrD, the relative suitability of EOS remains consistent. Further, EOS obtained from DFT are more precise in calculating difficult-to-measure properties such as the pressure derivative of the bulk modulus, and can recreate pressure driven phase transformations in polymorphic systems. This suggest that a large database of EOS will be capable of providing insight into pressure driven phase stability in systems yet to be explored by experiment.

8:00 PM - TC02.07.04

Capturing Solid Solutions During a First-Order Phase Transition of Li1+XMn2O4

Lithium-ion batteries (LIBs) offering the highest energy density among the known battery chemistries are the major contenders for both transportation and stationary storage applications. In order to satisfy the demands of energy density for these applications, new full cell configuration with either improved working voltage or specific capacity is needed to further enlarge its energy density. One candidate that has received a great deal of attention is the spinel cathode LiMn2O4, which offers the advantages of a high operating voltage (4.0 V vs. Li+/Li) and an excellent rate capability. Nonetheless, the relatively low specific capacity of 125 mAhg-1 is mainly due to the restricted operating voltage between 3 and 4.5 V. In theory, LiMn2O4 cathode can deliver a capacity of ∼297 mAhg-1 when 2 mole of lithium ions are inserted/extracted into/from both 8a tetrahedral and 16c octahedral sites of the spinel lattice at the voltages of, respectively, ∼4.0 and ∼2.7 V.1 Phase transition related to 4.0 V plateau is highly reversible, involving only two similar cubic spinel phases. However, phase transition related to 2.7 V plateau is partly reversible because a cubic spinel transforms to a tetragonal spinel with Jahn-Teller distortion occurring as a result of Mn3+ formation. The increase in the axial ratio from c/a = 1.0 in the cubic phase to c/a = 1.6 in the tetragonal phase due to the cooperative Jahn-Teller distortion leads to a fracture of large particles, which induces a loss of electrical contact with the current collector upon cycles.2 These effects cause serious capacity fading. However, the dynamic process of this phase transition has never been fully understood due to a lack of characterization techniques.Based on the above considerations, we report an in operando neutron diffraction study to fully understand the ~2.7 V related phase transition in the Li1+xMn2O4 spinel upon electrochemical cycling. We found solid solution formation upon reversible discharge and charge process, although a first-order phase transition is widely believed. The solid solution formation is possibly due to a thick electrode configuration that we applied and a large overpotential it could generate, which is cosistent with the phenomenon that observed under high-rate charging/discharging of LiFePO4 using in situ synchrotron XRD.3

The monoclinic phase (P21/c) of hafnium oxide (HfO2) is the most stable phase at room temperature and standard pressure; however, in many microelectronic applications, other phases of hafnium oxide are more desirable. For example, the tetragonal phase of hafnium oxide (P42/nmc) has a very high dielectric constant (κ=75) and a large bandgap (Eg = 6 eV), which is useful in transistor gate oxide and high-κ DRAM capacitor applications. Also, in the orthorhombic phase (Pca21), hafnium oxide can demonstrate ferroelectric behavior, and could thus form a central component of a new class of dense, non-volatile memory as well as high performance transistors.

The annealing treatment of hafnium oxide layers grown using atomic layer deposition (ALD) plays a central role in establishing the final crystal structure of the film. For example, it has been shown that annealing temperature profiles featuring a fast ramp rate can result in the suppression of the monoclinic phase of hafnium oxide in favor of the tetragonal or orthorhombic phases. Explorations of the mechanisms underlying the transformations of hafnium oxide during annealing could elucidate processing conditions that could give rise to the desired phases.

We use synchrotron radiation to perform grazing-incidence x-ray diffraction (GI-XRD) at SLAC/SSRL to study the phase transformations of ALD hafnium oxide insitu during annealing in a rapid thermal processing (RTP) chamber. We show that in metal-insulator-metal structures, a non-monoclinic phase crystallizes first during heating, with a strong monoclinic signal emerging when a slow ramp rate is used or when the film is maintained near its initial crystallization temperature for too long. We discuss the mechanism underlying this behavior, provide practical approaches for annealing hafnium oxide to suppress the monoclinic phase, and discuss the electrical properties of films annealed using these approaches.

8:00 PM - TC02.07.06

In Situ Measurement of Surface Relief Induced by Ferrite Plate Formation in a Low Carbon Steel by Digital Holographic Microscope

The mechanism of the transformation from austenite to ferrite plate in steel is an unresolved issue and discussions still continue to this day. Diffusion and shear mechanisms are conflicting two theories and both of them can rationalize most of experimental facts in the past. Surface relief on pre-polished specimen is one of the features of ferrite plate transformation and many researches have tried to reveal the mechanism by analyzing its shape. They measured surface reliefs at room temperature and classified their cross-sectional shapes into two types, tent-shaped type and invariant plane strain (IPS) type. The former is associated with the diffusional transformation and the latter with the shear mechanism. However, these conventional measurements after whole transformation process cannot distinguish the movement of surface purely by ferrite plate teansformation from another. Therefore, in-situ measurement on surface relief formation at high temperature is indispensable to reveal surface reliefs induced only by ferrite plate formation. We applied digital holographic microscope (DHM) for the first time to in-situ measure surface relief induced by ferrite plate formation.The alloy studied has the chemical composition Fe-0.15C-1.44Mn (wt.%). The specimens of 2 mm x 2 mm x 1.5 mm (length x width x depth) were cut out and their upper surfaces were mirror polished. The specimens were set in an infrared heating box, and heat-treated in Ar-3%H2 mixed gas atmosphere. The temperature was raised to 1473 K at a rate of 10 K/s and kept for 10 s, and then cooled continuously at 5 K/s. During the cooling process, surface relief was in-situ measured by DHM through the window on the top of the heating box. After the heat treatment, EBSD analysis on the area observed by DHM was conducted in order to specify the habit plane of each plate.The DHM system was able to capture at 50 fps, and measure undulations as precise as AFM. Both tent-shaped and IPS reliefs were observed and tent-shaped type was larger in number. In both cases, the relief got taller with a constant inclination of surface plane throughout the growing process. But, subsidence was observed on one side of some plates during thickening process. It was revealed that the final shapes of surface relief are formed after such changes. EBSD analysis identified habit plane of each plate and the angle between habit plane and the surface of the specimen. Assuming ideal displacive transformation, the ratio of the width and the height of the plate can be calculated. The measured ratio of IPS type relief is much smaller than the expectation. A more detailed discussion will be given in the presentation.

8:00 PM - TC02.07.07

In Situ X-Ray Diffraction Studies of Crystallization Growth Behavior in ZnO-Bi2O3-B2O3 Glass as a Route to Functional Optical Devices

Technology is currently striving to improve the power density of batteries, and to do so it is imperative to develop new materials, chemistries and manufacturing strategies. However, before all these proposed potential applications can be realised it is crucial to understand the fundamental processes taking place during materials synthesis, processing and electrochemical characterisation. The response of the material to electrical stimuli often determines the functionality, behaviour and performance in energy storage applications. Consequently, determining the correct structure–property–function relations requires a detailed description of the material in its working state. During the course of charging and discharging, a number of processes occur simultaneously, such as SEI formation, redox reactions, swelling and fracturing of electrode materials, etc; we focus on the SEI formation and swelling of our material in this work.

To this end, the primary objective of this work was to examine the electrode-electrolyte interface of an electrode material could be analysed by operando liquid-cell TEM imaging during the charge-discharge process. This experimental approach has effectively allowed for our TEM to be used as a “nano-laboratory” for carrying out dynamic electrochemical experiments on a small spatial scale. The active materials under observation in our experiments are Si nanoparticles and a Si-Graphene composite as a working electrode, and LiFePO4 counter electrode; both materials have been deposited on the electrodes of our specialized electrochemistry TEM chip via inkjet printing methods[1]. Si was chosen due to its potential as a high capacity anode material, and high volumetric expansion upon lithiation [2]; thus any changes in structure would be evident.

During our study of the operating cell, a number of barriers to accurate observation of the operation of the electrodes have been encountered, most notably the beam-sensitivity of the organic electrolytes used in the electrochemical setup. The cell was tested with a number of different lithium salts and solvents (ranging from conventional LiPF6 in EC:DMC, to LiTf in DO) for use as a suitable electrolyte in an attempt to limit lithium dendrite formation and undesired reduction of electrolyte as a result of electron beam illumination [3]. In spite of the shortcoming, we believe that it is possible to use the proposed system as a novel characterisation method for a range of new materials in their operating environments.

Atomic position in a unit cell determines the functionalities of complex oxide thin films; e.g., remnant polarization or piezoelectric coefficient in ferroelectrics. Exploring of the atomic movement under external electric field and/or stress, accompanying with a change of polarization, polarization switching, and lattice expansion, has been demanded in order to artificially manipulate functionalities of materials; however, in situ observation of atomic movement in complex oxide thin films under external stimuli has been limited mainly by an exponential increase in leakage current component during a long-time experiment and/or extrinsic effects arising from variation of substrate and film thickness. Systematic in situ studies excluding these extrinsic effects on atomic movement under external stimuli is critical to understand an intrinsic role of atomic position for functionalities of complex oxide thin films.

Here we report on in situ observation of atomic movement in BiFeO3 thin film under external electric field and stress. In our experiments, we used time-resolved X-ray microdiffraction (TRXμD) technique to monitor both the reflected X-ray intensities arising from atomic position as well as the lattice parameter of film. We found an excellent agreement between experimental results and density functional theory predictions for atomic movement under electric field on BiFeO3 thin film. Under an application of electric field to film, both experimental and theoretical results show that displacement of oxygen atoms in BiFeO3 film is larger than that of Fe atom [u1] during ferroelectric switching and increase of polarization. We also found that the external stress increased relative position of Fe atom in contrast to the results from application of electric field to film due to the consideration of relative movement of Fe atoms inside a unit cell. We found that distance between Fe atom and oxygen atom is a key factor to determine polarization in BiFeO3 thin films rather than simple displacement of center atom and/or tetragonality of unit cell. In addition, we found that application of external stress on ferroelectric film could induce atomic movement different from results of applied electric field even though the lattice parameter varies in similar manner for both stimuli.

8:00 PM - TC02.07.10

Express-Method for the Study of Electrolyte Anion Profiles in the Bulk of Dense Anodic Alumina Films

The detailed study of the growth behavior of anodic oxide films is impossible without reliable information about electrolyte anion profiles in the bulk of the forming oxide. The widely used methods such as X-ray photoelectron spectroscopy, Auger spectrometry, secondary-ion mass spectrometry, etc. have limited accessibility, are time-consuming and not always suitable for studying the metal-electrolyte system since to provide analysis with these methods the sample should be taken away from the electrolyte and placed into a vacuum chamber. It is of practical significance to have at hand the express-method that allows recording valid data on the composition uniformity and certain presence of foreign ions and their penetration depth into the oxide film for next more effective and purposeful use of expensive methods. Moreover, a method is needed to obtain information about anion profiles in thick, more than hundreds nanometers, layers in reasonable time.To develop such the method, we draw our attention to the well-known method for the chemical dissolution of oxides and to the fact that the presence of the oxide film, even of the tunnel thickness, on the metal surface changes its electrode potential. When a pure metal electrode or the metal electrode covered with the oxide film is placed into the electrolyte, a certain potential relative to the reference electrode is established on its surface. This potential is inherent to given metal in a given solution. The value of the potential depends on the type and the energy state of the surface monolayer atoms and is an average statistical value of potentials of local microranges (at the limit of ions) at the electrode-solution interface. So, it is evident that the electrode potential of pure oxide differs from the potential of oxide with introduced electrolyte anions. Therefore, if the sample with oxide to be measured is placed into the solution dissolving the oxide moderately and a time variation of the electrode potential is read, very important information on the anion presence and anion profiles in the oxide film can be obtained. A shift of the electrode potential measured from the steady-state potential of pure oxide depends on the concentration and the energy-state distribution of surface atoms and can be expressed using the so-called sum of states, i.e. simply by the sum of members defining a number of atoms in every energy state Eitaken over all energy states:Σ Gi exp(-Ei/kT),where Gi is the surface concentration, Ei is the energy level of the i surface atom.Thus, by measuring the variation of the steady-state electrode potential during the oxide etching, some potential profile of practically each monolayer can be obtained.The method developed can be used to study a chemical evolution in anodic alumina formed to correlate with modeling and simulations across materials science disciplines.

8:00 PM - TC02.07.11

New In Situ, Thermal Radiation, and Stray Light-Immune Stress and Thick Layer Metrology for Research and Production of Novel Materials

Wojciech Walecki 1 , John Groot 1 1 Research and Development, Frontier Semiconductors, San Jose, California, United States

We present a family of techniques for in-situ characterization of novel materials. The family includes three novel technologies: (A) a novel stray light, and thermal radiation insensitive tool for measurement of the stress in growth and processing chambers, (B) thick and thin film metrology tool for in-situ monitoring of deposition or etching process operating in novel oblique angle configuration. Both these patent pending technologies can be combined and operate together through the same process chamber window, and they be also combined and operated simultaneously with oblique angle scatter, which was already presented at MRS Spring show this Spring [1].

The technique A is an improvement on the idea of employing a set of parallel beams for probing changing curvature of wafer presented by E. Chason in his patent [2]. Unlike as it is described in [2] , we are using set of modulated beams each having different frequency. The parallel beams are reflected from the measured sample, and reflected beams are impinging a position sensitive detector (PSD). Since the PSD is an linear analog device and since it is possible to detect position of each beam separately using frequency filtering techniques. In our case we propose use of phase sensitive (lock-in) detection technique to achieve perfect separation of signal and noise rejection [3-5].In addition our technique allows of use of multiwavelength beams eliminating and minimizing possibility for deterioration of the reflected beam due to destructive interference in certain coatings.

Our methods provides following improvement over traditional system described in Chason patent [2]:1. Eliminates stray light by use of multichannel lock-in2. Enables measurement of several light beams simultaneously3. Pixel nonuniformity issues and4. Use of fiber-optic beam couplers allows perfect alignment of multicolor beams

In addition we describe use of low coherence fiber optic interferometry for measurement of thickness of thick and thin layers in a grazing angle configuration, and discuss benefits of combining this technology with stray light insensitive stress metrology discussed above.

Nanoparticles (NPs) exhibit differences in atomic, electronic, magnetic, physical and chemical properties compared to their bulk, due to quantum confinements effects associated with nano-sized dimensions. Research on NPs at extreme conditions such as, at high pressure and temperature environments has seen further modifications of these properties. Iron-oxide magnetite (Fe3O4) is a naturally occurring magnetic material, whose particles in the nano-sized region are studied extensively for advancements in medical, biological, electronics and planetary research. We investigate how increasing pressure (up to ~20 GPa), contribute to any modifications in structural and magnetic properties of 6 nm magnetite (Fe3O4) NPs. Similar investigations on bulk magnetite have been conducted previously, however, only a little is known regarding NPs. Magnetite NPs are prepared using controlled chemical coprecipitation technique and are characterized by x-ray diffraction, transmission electron microscopy, Raman Spectroscopy, x-ray photoelectron spectroscopy and are tested for magnetic properties. We use synchrotron techniques, x-ray magnetic circular dichroism (XMCD) and x-ray absorption spectroscopy (XAS) at Fe K-absorption edge, to investigate magnetic and structural properties of NPs up to ~20 GPa, using diamond anvil cells at room temperature conditions at the Advanced Photon Source (APS), Argonne National Laboratory. The results of magnetic and structural transitions in magnetite NPs with increasing pressure conditions will be presented.

Bulk techniques that analyze thermal transformations in materials, such as calorimetry, give an averaged response of the complete transformation, missing distinct events in aggregates or inhomogeneous materials. Capturing different transformation paths is particularly important when studying nanoparticles or devices that have at least one nanometer-sized functional dimension, because it is known that transition temperatures are size dependent [1,2]. In-situ TEM heating holders provide a platform to observe thermal transformations with high spatial resolution—even atomic resolution. With this technique, distinct localized microstructural changes can be detected within a global transformation in a particle by particle basis.

The so-called in-situ bulk heating TEM holders comprise a small furnace compatible with 3mm TEM grids, but a newer approach uses microfabricated micron-sized heating elements to heat the sample under observation. This latter option has advantages: the power required to heat a sample is about 3 orders of magnitude lower; faster heating and cooling rates; and natural compatibility with microfabricated devices.

Here we present in-situ TEM observations of the heat-induced cubic to hexagonal phase transformation of NaYF4 nanocrystals (< 50nm wide) at temperature > 300°C. This phase transformation is accompanied by a depletion of material from the center of the nanocrystals. We discussed the observed hollowing effect by highlighting the importance of tracking individual particles during phase transformations. This is made possible using an in-situ heating TEM holder with microfabricated heating elements. The heating elements are patterned into a removable chip containing an electron-transparent window where the sample is deposited. The holder contains 9 electrodes that control the temperature and provide optional biasing capabilities to bias a sample (or device) during heating, if needed. Our observations were performed on a TEM operated at 200kV (JEOL JEM 2100) and equipped with a direct electron detection camera (Direct Electron DE-12) with 24 frames per second rate at full frame (4k × 3k pixels), which allows us to capture structural changes in discrete nanocrystals within 1 second.

X-ray diffraction is typically limited to crystalline materials. This poster will explore two methods for using Rietveld Refinement to quantify imperfect crystalline materials. AgxFeOy is used as an example system. Perfectly crystalline AgFeO2 forms one of two similar structures, which only differ in terms of plane stacking behavior.Using high-resolution synchrotron data we show that neither the hexagonal nor the rhombohedral crystal structure provides adequate fits of the diffraction data. We develop a new model using DIFFaX software. We also show a method to refine the stacking fault structure using GSAS II.Using a mixture of complementary techniques, including Raman spectroscopy and XAFs, we show that AgxFeOy where x is small is a composite material with a significant maghemite (Fe2O3) component. We show a simple method for quantifying the silver ferrite and maghemite phases using Rietveld Analysis. The results agree well with the synthetic parameters, and help to explain the special electrochemical behavior of the composite material.

Laser assisted chemical vapor deposition (L-CVD) provides the means to deposit high quality, crystalline and conformal films with a high degree of spatial control. Fully harnessing the capabilities of L-CVD requires a detailed understanding of the relationship between the structure/composition of the deposit and the process conditions. Identifying these relationships using ex situ, Edisonian, approaches is an arduous process, involving exploration of a matrix of numerous parameters that include the substrate temperature, laser prower, and gas compositions and pressure. The development of in situ/operando structural diagnostics is, therefore, essential for the rapid evaluation of the effects of varying deposition conditions. An operando x-ray diffraction/ x-ray absorption system is used for rapidly elucidating optimal LCVD growth conditions of crystalline boron-carbon materials using trimethyl borate precursor. Trimethyl borate exhibits vastly reduced toxicological and flammability hazards compared to existing precursors but has previously not been applied to boron carbide growth. The use of the operando x-ray diffraction system allows for the exploration of highly non-equilibrium conditions and rapid process control, which are not possible using ex situ diagnostics. The presence of hydrogen at elevated temperature was shown to be critical in the production of boron-carbide. The ability to observe reactions during operation allows the characterization of transient boron carbide (B8C phases) that would not be observed ex situ and limits the need for arduous processing routines.

We have also conducted a series of operando synchrotron-based x-ray absorption experiments that interrogate the L-CVD growth of Silicon Carbide (SiC). SiC was grown from tetramethylsilane using a CW 532nm YAG to achieve laser-based pyrolytic precursor decomposition. The change in the SiC electronic structure was measured during LCVD using a Auger electron yield gas cascade detector with allowed surface sensitive XAS measurements to be made under operando conditions. By monitoring the Si K-edge (1.8keV) x-ray absorption one could measure the change in the electronic structure of the SiC as a function of laser power, substrates, and pressure conditions. These results demonstrate a platform for accelerated implementation of novel CVD precursor systems and a method for process control under conventional growth recipes.

This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC5207NA27344. Project 14-ERD-067 was funded by the LDRD Program at LLNL. This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Crystalline materials that behave as optical actuators and proceed via some form of nano-optomechanical mechanism are of particular interest for optical data storage[1] or quantum computing[2]. Nonetheless, the field is facing a dearth of suitable functional materials for applications. One possible material option is a series of compounds based on the generic formula, [Ru(SO2)(NH3)4X]Y, whose SO2 group manifests solid-state linkage photo-isomerization (X is the trans-ligand to SO2; Y is a counterion). This light-induced phenomenon causes these materials to act as photo-induced molecular switches [3-5] or molecular transducers [6,7] whose nano-optomechanical properties exist in the single-crystal state: a high-quality solid-state medium for single-photon control.

This talk will present the development of this family of materials towards such applications, via a range of advanced in situ 'photo-crystallography' and in-situ imaging experiments that capture the phenomenon in their light-induced state [8-10]. Results are enabling our understanding of the light-induced molecular structure and nano-optomechanical properties of these light-induced solid-state actuators. Establishing this knowledge-base of structure-to-function relationships leads to the ultimate goal of being able to molecularly engineer these materials for a given device application.

Al/Zr reactive nanocomposite powders show promise as a fuel additives in bio-agent defeat applications where long burn times and high heat output is necessary to decontaminate anthrax spores. The powders are generated via high energy planetary ball-milling, and they have independently tunable ignition and combustion properties through variations in reactant spacing and particle size. Using synchrotron x-rays at the Advanced Photon Source (APS, 32-ID-B), we have viewed the interior of the combusting particles via phase contrast imaging. Once ignited on a hot-filament, the particles fall off and burn in both vapor and condensed phases at 2700-3500 K and violently microexplode. Several burning particles have been observed throughout their entire combustion lifecycle that includes the formation of an Al-Zr intermetallic molten solution, the evaporation of Al and the formation of AlO, the transition to a liquid Zr-Al-N-O solution, the heterogeneous nucleation and growth of bubbles in the liquid particles, and violent microexplosions when the bubbles expand rapidly. We will present observations of the heterogeneous nucleation sites, growth rates of the gaseous bubbles, velocities of the fragments resulting from the microexplosions, and morphologies, chemistries, and wall thicknesses of the final hollow shells that do not explode. Through simultaneous external high-speed imaging and spectroscopy, we can correlate internal bubbling observations with visible luminous intensity spikes, gaseous production, and average plume temperatures. Together, these observations provide a deeper understanding of the combustion process and a basis for optimizing combustion performance.

8:30 AM - *TC02.08.03

In Situ X-Ray Diffraction Studies on the Effect of Ferroelectricity During the Growth of Ferroelectric Multilayers

In epitaxially strained ferroelectric thin films and superlattices, the ferroelectric transition temperature can lie above the growth temperature. Ferroelectric polarization and domains should then evolve during the growth of a sample, and electrostatic boundary conditions may play an important role. In addition, ferroelectric polarization can play a role in strain relaxation mechanisms. In order to study these effects we have used in-situ x-ray diffraction during the growth of ferroelectric multilayers at X21 at NSLS and now at ISR at NSLS-II at Brookhaven National Laboratory.

Polarization during growth manifests itself in a particularly interesting way in PbTiO3/BaTiO3 superlattices grown by off-axis RF magnetron sputtering on SrTiO3 substrates. As both components of the superlattice are ferroelectric and have elevated transition temperatures due to compressive strain from the substrate, a number of characteristics of the superlattices are extremely sensitive to layer thickness and growth temperature. For example, the as-grown polarization domain structure, as measured by piezoforce microscopy, is markedly different depending on whether the overall structure’s transition temperature lies constantly below, constantly above, or oscillates around the growth temperature. Perhaps more surprisingly, we have also found that the ferroelectric polarization of a growing structure has a strong effect on the rate at which it grows, which is critical information if high quality samples with well-defined layer thicknesses are to be achieved. We have studied this effect in detail by focusing on the properties of BaTiO3 thin films grown on very thin layers of PbTiO3 using a combination of x-ray diffraction, piezoforce microscopy and electrical characterization. The relaxation dynamics during growth and their connection to polarization are revealed by performing rapid reciprocal space maps around the (1 0 1) peak during the growth and we show that these are intimately connected with the eventual properties of the films.

In BaTiO3/SrTiO3 superlattices grown on SrTiO3, rather than relaxation of strain the focus is on the evolution of ferroelectric domains, surface termination, average lattice parameter and bilayer thickness, which we simultaneously monitored using in-situ synchrotron x-ray diffraction during the growth. Effects of electric boundary conditions were investigated by growing the same superlattice alternatively on SrTiO3 substrates and 20nm SrRuO3 thin films on SrTiO3 substrates. These experiments provided important insights into the formation and evolution of ferroelectric domains when the sample is ferroelectric during the growth process.

Interfacial science by its very nature brings together diverse interests in areas such as: electronic materials, oxide film growth, nano-science, biomembranes, geochemistry, surface physics, catalysis, and electrical-energy storage. Sophisticated in situ synchrotron X-ray methods are developed to understand the assembly of atoms, molecules and supported nanoparticles at interfaces in complex environments. Examples will include the use of X-ray reflectivity (XRR), X-ray standing waves (XSW) and X-ray photoelectron spectroscopy (XPS) for studying interfaces such as growth and chemical reactions involving metal nanoparticles and monolayers on oxide surfaces.

9:30 AM - TC02.08.05

An In Situ Study of the Perovskite to Brownmillerite Phase Transition Using a Novel Time-Resolved X-Ray Reflectivity Technique

Brownmillerite (BM) phases, having an ordered oxygen vacancy sub-lattice, have higher oxygen conductivity than their perovskite (PV) counterparts, making them an attractive cathode material candidate for solid oxide fuel cells. Recently, Ferguson, et al. [1], employed synchrotron-based in-situ scattering, especially x-ray reflectivity (XRR), to demonstrate a transition from the PV (x=0) to BM (x=0.5) phase in a buried epitaxial thin film of La0.7Sr0.3MnO3-x (LSMO) on SrTiO3 (STO). This transition is induced by deposition of oxygen-poor STO on top of the LSMO film. However, many details, such as the role of strain and domain morphology in driving or inhibiting the transition, could not be characterized. Because the transition only proceeded above a certain STO growth rate and the BM reverted to the PV phase when the transition was halted below a certain volume fraction, traditional Parratt XRR (requiring sequential collection of different scattering angles) lacked sufficient time resolution to capture these details. Alternatively, XRR at a single angle – e.g. the Anti-Bragg condition – provides insufficient information to monitor either the lattice parameter or domain thickness of the BM phase.Here, we present a new study of the PV-to-BM phase transition of LSMO on STO based on a novel method of time-resolved XRR for use with monochromatic synchrotron radiation. The method uses a half-focusing polycapillary x-ray optic to create a planar converging fan of radiation incident on the sample. The diffracted intensity, which is dominated by the specularly-reflected rays, is collected on an area detector, permitting the simultaneous collection of a portion of the reflectivity curve. In particular, we demonstrate parallel collection of XRR data over a range of 5° in 2θ, with the ability to obtain time resolution down to 100 ms and resolve Kiessig fringes from films ranging in thickness from 3 to 76 nm.Using this technique we have successfully collected reflectivity curves during the PV to BM transformation covering around one third of a Brillouin zone around the half-order Bragg peak resulting from the oxygen vacancy sub-lattice. This range is sufficient to concurrently determine the intensity, position, and Kiessig fringe spacing of the BM-phase Bragg peak, providing a fuller picture of the transition. We observed two distinct transition pathways. In one case the BM phase appears as a continuous thin layer with its final out-of-plane lattice parameter, whose thickness then increases. In the second case, the BM domains quickly reach the full thickness of the LSMO film, and then grow laterally outward. As the ratio of BM to PV phase increases, the BM domains are able to relax as shown by a change in the Bragg peak position during the transformation.[1] J. D. Ferguson et al., "Epitaxial Oxygen Getter for a Brownmillerite Phase Transformation in Manganite Films," Advanced Materials, vol. 23, pp. 1226-1230, 2011.

9:45 AM - TC02.08.06

Understand the Formation of Metal Nanoparticles with In Situ XRD and Ab Initio Computation

Phase diagrams are the maps for the design and synthesis of functional materials. However, the bulk phase diagrams oftentimes are not predictive in the synthesis of nanostructures of many functional materials owing to the significant contribution of surface energy at nanoscale. This work aims to quantify how the surface energy varies the total energy, and therefore alters the phase diagram in given compositional or temperature windows, with using metallic cobalt as a model system. The formation of Co nanoparticles in its two polymorphs, namely, the face-centered cubic phase (fcc) and the hexagonal close-packed phase (hcp), in solvothermal reactions was investigated both computationally and experimentally. Cobalt precursors can be precisely tuned to form either one of the polymorphs in solvothermal reactions by controlling the pH and using surfactants. Novel synchrotron-based in situ X-ray diffraction (XRD) for solvothermal reaction technique was used to track the nucleation and ripening processes of the nanometric Co to elucidate the thermodynamics and kinetics of these processes. First-principles Density Functional Theory (DFT) computations were used to theoretically quantify the change of the surface energies of Co nanoclusters with different capping agents for different facets, particle sizes, and pH values. The experiment and computational results together indicated that by investigating the surface energy of nanoparticles, phase diagram of Co at nanoscale can be understood and predictively constructed under different synthesis conditions. This approach is possibly to be generalized to offer guidelines for the design, synthesis, and property tuning of many functional materials.

The discovery and analysis of X-ray diffraction from crystals by Max von Laue, William Henry Bragg and William Lawrence Bragg in 1912 marked the birth of X-ray crystallography. Over the last century, X-ray crystallography has been fundamental to the development of many fields of science. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are non-crystalline, and thus their 3D structures are not accessible by traditional X-ray crystallography. Overcoming these obstacles requires the development of new X-ray sources and methodologies. Recently, the X-ray science community has witnessed two revolutionary developments. First, large-scale coherent X-ray sources, such as X-ray free electron lasers and advanced synchrotron radiation, have been under rapid development worldwide. Compared with previous generation X-ray sources, the new sources increase the X-ray brilliance by several orders of magnitude. Second, the methodology of X-ray crystallography was extended to allow the structure determination of non-crystalline specimens or nanocrystals in 1999, which is known as coherent diffractive imaging (CDI) or computational microscopy. In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In this talk, I will give an overview on how the combination of coherent X-ray sources, CDI methods and high-speed detectors opens up new and important opportunities for in situ studies of material systems.

Additive manufacturing (also known as “3D printing”) is an emerging technology that takes part in all the academic and industrial disciplines. Currently, broad research is being done on the many possible applications which can be produced with this technology. Fused deposition modeling (FDM) is one of the printing technique which used thermoplastic polymer filaments which being deposited layer on top of layer to form final desired product.There is high demand today for lightweight materials with enhanced mechanical, thermal and electrical properties. Oriented graphene in polymeric matrix can enhance the thermal, mechanical and electrical properties of printed products in FDM technology [1, 2]. In addition, it can help to efficient printing process by controlling the rheological and the thermal conductivity properties of the polymer melt.In this study, we prepared filaments of polypropylene and graphene nano-sheets in different weight ratios. In situ small and wide angles x-ray scattering measurements of the filaments extrusion process were done on beamline 12BM at the Advanced Photon Source in Argonne National Laboratory. The measurements were done on melt extruded filament through nozzle as in the FDM 3D printing process. Thermal imaging of the extrusion process was done by thermal infra-red camera. In parallel, simulation of the temperature and velocity profiles in the extrusion process was done by method of Lattice Boltzman Modeling.We show that right after the exiting the nozzle, the polypropylene filaments has no crystalline structure when extruding at nozzle temperature above 170 C. However, few seconds after the extrusion process stops, the polypropylene filament crystallizes with extrusion axis orientation. The addition of graphene nanoparticles causes phenomena of transcrystallization where the polymer chains crystalize on the surface of the graphene nanoparticles. Azimuthal angle scan shows matched orientation of the polypropylene (040) plane together with the graphene.Raman spectroscopy analysis was done to verify the dispersion of the graphene particles in the polymer matrix. Thermal analysis of the composite was done by differential scanning calorimetry. Finally, the composite filaments were tested in 3D printing and the thermal, mechanical and electrical properties of the printed structures were tested.

The advantages and capabilities of additive manufacturing (AM) initiated a renaissance in American manufacturing by decreasing costs, increasing energy efficiency, enabling new component design motifs, and providing a manufacturing pathway for novel materials which cannot be processed by traditional means. However, much is still unknown about the starting material properties and the processing parameters on how they relate to the final printed part. The final material of the printed parts is dependent on these parameters and an experimental study of the building process is necessary to fully understand part performance. By utilizing the high brilliance X-ray source at the Stanford Synchrotron Radiation Lightsource at SLAC National Accelerator Laboratory, a high-speed imaging system was developed for observing the additive manufacturing process. The imaging system has demonstrated successful high-speed imaging of the build process in a powder bed selective laser melting AM chamber while the laser is melting the powder. The recorded X-ray images provide valuable information about the process by nondestructively transmitting through the sample so that void formation, keyholes, and melt pool are visible during the build. By controlling build parameters, e.g. laser power, spot size, laser speed, X-ray images of the newly built track, powder bed, and substrate will provide crucial information necessary for increasing the accuracy of simulations to help inform the build process, material properties, and part design.

Carbon fiber (CF) exhibits a unique combination of material properties, including high tensile strength and modulus, low weight, high temperature resistance, and low thermal expansion. The unique combined properties of this material are a direct consequence of its constituent highly-oriented graphitic microstructure, which is typically obtained commercially through controlled pyrolysis of either polyacrylonitrile (PAN) or mesophase pitch-based fiber precursors. Current precursors and conversion processes are expensive, and limit the low cost potential of CF to $10/lb, which has thus far precluded its wide-spread adoption in automotive and industrial markets. Polyethylene is a promising precursor to enable a high volume industrial grade CF as it is low-cost, melt-spinnable, and has a high carbon content. However, sulfonated polyethylene-derived carbon fibers (SPE-CFs) have thus far fallen short of the 200 GPa tensile modulus threshold for industrial applicability. Here we present a graphitization process catalyzed by the addition of boron that produces carbon fiber with > 400 GPa tensile modulus at 2400 °C. To better understand the fundamental processes occurring during graphitization, and the structure-property-process relationships for these very different precursor materials, measurement of the characteristics of the graphitic microstructure, such as orientation, domain size, and interlayer spacing is critical.This presentation will describe the design and operation of a custom high-temperature tensile device that, when combined with synchrotron wide-angle x-ray diffraction (WAXD), enables us to observe in situ and in real time the microstructural transformation from carbon fiber precursor to high-modulus carbon fiber. Specifically, this tensile device heats fiber bundles from 25 °C to greater than ~2300 °C, while simultaneously applying tensile stress, and monitoring the resulting fiber strain. Synchrotron WAXD patterns obtained as a function of temperature reveal the conversion to graphitic microstructure, and provide key insights into the physical processes that occur during carbonization and high-temperature graphitization. Experiments conducted using PAN-, pitch-, and boron-doped PE-derived fiber precursors reveal stark differences in the carbonization and high-temperature graphitization behavior among these precursor types. Surprisingly, it was found that the presence of boron reduces the onset of graphitization by nearly 400 °C, beginning at ~1200 °C for SPE-CF precursors. The B-doped SPE-CFs herein attained 200 GPa tensile modulus and 2.4 GPa tensile strength at the practical carbonization temperature of 1800 °C.

Superconductors with mesoscale ordering and porosity may have properties very different from their bulk counterparts, including increased critical fields and novel flux pinning behavior. The exploration of these properties is limited by the routes to produce such mesoporous superconductors; currently the only synthesis involves a poorly-understood two-step treatment of block copolymer-derived mesoporous niobium oxides under flowing ammonia gas at temperatures above 850 C to produce superconducting niobium nitride with a critical temperature about half of its best-reported bulk equivalent. We have used in situ small- and wide- angle X-ray scattering in combination with XANES during these annealing steps to probe the pathway complexity of this transformation and enable both improved mesostructure quality and superconducting properties approaching those of bulk niobium nitride, paving the way toward block copolymer-inorganic hybrid co-assembly as a scalable, tunable platform for exploration of the impacts of mesoscale order and porosity on superconducting properties.

Many materials of interest in energy-related applications interact strongly with their constituents and environments, leading to complex interrelationships between structure, composition and bonding, all of which can change continuously during reactions. To address this complexity, it is highly desired to move beyond conventional transmission electron microscopy (TEM) projection imaging. Because projection images can be misleading or inconclusive for inhomogeneous systems, there is a dire need in the materials research community to track material changes in all three spatial coordinates with high time resolution at the nanoscale. However, a stumbling block is the rather slow process of acquiring electron tomography (ET) data to allow retrieval of depth information at the relevant length scales. In this talk, I will report the realization of high temporal resolution electron tomography, on-the-fly reconstruction, and the first attempt to achieve five-dimensional (5D) electron microscopy data sets under reaction conditions. The 5D data sets visualize the oxidation of a Co-Fe catalyst with unprecedented 3-D and chemical details and transform our understanding of adsorbate induced segregation in bimetallic systems.

Over the last twenty years, colloidal nanoparticles have evolved into a major building block for solid state chemistry and the design of materials. Today, such nanocrystals are in practical use in catalysis, displays, and electrical applications. Understanding details of atomic structures and changes of nanoparticles during growth, structure changes is very important since they determine physical and chemical properties of nanoparticles. In addition, as-grown nanoparticles are known to undergo dynamic phase transitions while they are used in diverse chemical conditions. However, most of nanocrystal synthesis and their practical uses are developed empirically with a limited mechanistic understanding. Due to their small size and heterogeneity, static and dynamic structure information of nanoparticles in their native solution phase cannot be easily accessible by conventional analytical methods. The recent advent of the in-situ liquid cell for transmission electron microscopy is just such a tool. We observe the diffraction patterns from individual Pt nanoparticles as they rotate in the liquid cell, and ultimately, we are able to align and invert those images to obtain the 3D atomic structure of individual particles freely moving in liquid. Positions of entire atoms composing an individual nanoparticle are identified onto 3D density maps. Such atomic positions unveil different degree of crystallinity in the core, grain boundary, and surface of a single nanoparticle. We also perform time-resolved 3D structure reconstruction of a nanoparticle while the particle undergoes structural changes in solution. The time-resolved 3D density map shows details of spatial fluctuation of individual atoms during structural transition of a single nanoparticle.

Traditionally, Kirkendall voids, created by the imbalance of interdiffusing species in a diffusion couple, are undesirable as they often result in degraded mechanical, thermal, and electrical properties. However, the Kirkendall effect can be used deliberately as an alternative route to fabricate small-scale hollow structures. For example, this can be achieved by coating a slow diffusing metal on the surface of a wire to create a core/shell structure and homogenizing it such that, during interdiffusion, there is an inward flux of vacancies toward the center of the sample. Due to the spatial confinement and radial symmetry of this geometry, the excess vacancies condense to form voids centrally located within the wire. If annealed under appropriate conditions, the pores coalesce and form continuous Kirkendall channels throughout the length of the wires, hence transforming them into microtubes.

We demonstrate here that this concept can be used to convert 50 micrometer diameter pack-titanized Ni wires and pack-aluminized Ni-Cr wires into Ni-Ti and Ni-Cr-Al microtubes, respectively. To be able to tailor the internal porosity, the mechanisms involved in, and the kinetics of the phase and void formation and evolution in both of these systems must be understood. Using an in situ non-destructive 3D visualization technique is critical to gaining insight as it provides the real-time, high temperature morphology of the voids. Therefore, a combination of traditional ex situ metallography and in situ synchrotron X-ray tomographic microscopy was used. Two different series of tomography experiments were performed at the Swiss Light Source and the Advanced Photon Source where in situ sample anneal was conducted via laser-based and resistance-based heating systems, respectively. While the resistance furnace provided a nominally isothermal annealing condition, under the localized heating of the laser a significant longitudinal temperature gradient was introduced on the wire sample, thereby resulting in void migration and altering the microstructural evolution.

Here we discuss the results of the tomography work and show that this is a viable technique to use in conjunction with more conventional ex situ metallographic experiments to conduct rapid diffusion studies. Once further developed, this Kirkendall hollowing approach could extend to other material systems with appropriate reactive diffusion kinetics and to the fabrication of more complex hollow geometries, which would offer low density, high specific mechanical properties, and high surface area making them good candidates for various structural and thermal applications.

The deformation behavior of metallic single crystals is size dependent, as shown by several studies during the last decade. Nevertheless, real structures exhibit different interfaces like grain, twin or phase boundaries. Due to the possibly higher stresses at the micron scale, the poor availability of dislocation sources and the importance of diffusion in small dimensions the mechanical behavior of samples containing interfaces can considerable differ from bulk materials. Within this study we will show the size scaling behavior of general high angle grain boundaries in copper. The boundary presented is believed to show extensive dislocation slip transmission at bulk dimensions.In the talk results from in situ scanning electron microscopy (SEM) and in situ µLaue diffraction will be shown. While the SEM data is used to proof slip transmission, µLaue is probing the occurrence of dislocation pile-ups at the grain boundary. The results show that at low plastic strains and strain rates the size scaling behavior of single and bi-crystalline samples is identical in cases where the grain size is assumed as the critical length scale. It can therefore be concluded that the initial number and size of dislocation sources is dominating not only the deformation behavior of single crystalline pillars, but also for bi-crystals (at low plastic strains). Thus, the character of the boundary does not play any role for the mechanical properties at the onset of yield during slow deformation. This behavior is vastly different when higher strain rates up to 10-1s-1 are applied. Then, the bi-crystalline sample shows significantly higher yield stresses.While at low strains and strain rates the initial source size is key for the deformation behavior, higher strains and strain rates hint towards the non-conservative motion of dislocations in the grain boundary plane as the limiting process. In the talk, this will discussed together with possible strategies to implement the experimental findings to discrete dislocation dynamics simulations.

4:00 PM - TC02.10.02/TC06.14.02

Use of In Situ TEM to Characterize the Deformation-Induced Martensitic Transformation in 304 Stainless Steel

Djamel Kaoumi 1 1 , North Carolina State University, Raleigh, North Carolina, United States

Tensile tests are conducted in-situ in a TEM at room temperature down to cryogenic temperatures (from -100°C to 0°C) using a cooling TEM straining-stage with the goal of capturing the growth of the martensitic phase as it develops under stress in the material. The formation of stacking faults was captured, as well as the subsequent formation of ε-martensite, confirming the role played by SFs as intermediate step during the transformation from γ-austenite to ε-martensite. In addition, direct transformation from γ-austenite to α’-martensite was captured as well (i) upon straining at a fixed temperature and (ii) upon cooling after pulling on the sample, indicating again how stress and temperature are both effective on the transformation.

Modern cold-forming processes subject metals to multiaxial stress states and strain path changes which are not accurately modeled using uniaxial mechanical testing. It is therefore important to examine the material behavior during the complex strain paths experienced in industry. Here, in situ diffraction techniques are used to study the influence of non-linear strain path changes on the deformation mechanisms, microstructure evolution and residual stress development of a cold-rolled Mg AZ31B with strong basal texture. Neutron powder diffraction with acoustic emission and Laue microdiffraction are used to link the bulk macroscale behavior of the alloy with specific deformation mechanisms observed at the microscale, in a single grain.The deformation behavior of the AZ31B was examined during three load path changes of 45, 55, and 90 degrees from a uniaxial preload using combined in situ neutron powder diffraction (POLDI beamline, SINQ) and acoustic emission. All loads were in-plane tension. The results show that the active strain accommodation mechanisms ({10-12}<10-11> extension twinning vs. basal slip) in the second load depend strongly on the angle of strain path change. Laue microdiffraction experiments were then performed (MicroXAS beamline, SLS) to examine active mechanisms within a single grain during bulk deformation of the polycrystal. The results are used to link the microscale behavior with the bulk properties observed in the neutron experiments, and more closely examine the role of strain path changes on twin variant selection. Additionally, EBSD and TEM images from various stages of deformation have also been prepared; the microstructure changes are examined with respect to the lattice strain evolution measured during the in situ tests.This research is performed within the ERC Advanced Grant MULTIAX (339245).

The ultrahigh strain rate behavior of lightweight energy-absorbing materials, such as glassy-rubbery block copolymers: polystyrene - polydimethyl siloxane (PS-PDMS), thin multilayer graphene films, polymer grafted nanoparticle films and single crystal silver microcubes, is explored using a miniaturized ballistic test: LIPIT, Laser Induced Projectile Impact Test. Micron sized projectiles are launched at various targets using a laser pulse, and the deformation field around the embedded projectile is analyzed for thick targets, while penetration occurs for thin targets and projectile deformation occurs in the case of a soft projectile/hard target. Such studies provide valuable information on how materials respond to very large strains at very high (~ 107 s-1) strain rates, important for applications such as advanced protective materials. The small size of the projectiles provides a deformation field that is < tens of microns in size and can be examined at high resolution. Characterization is done by a combination of dual SEM and ion beam microscopy as well as TEM of thin slices. Correlation of these micro scale tests to models as well as how the behavior scales to the macroscale are being explored.

X-ray topography is a well-established method to visualize dislocations and associated strain fields in single crystals. It is based on Bragg diffraction and provides a two-dimensional intensity mapping of the diffracted beam. The resolution is typically limited by the pixel size of the detector, which restricts its practical usage to relatively large objects and defects. In this work we present a new method, ptychographic topography, where we combine tele-ptychography and Bragg topography. In tele-ptychography an object is illuminated with a parallel x-ray beam and the wave front after propagation through the object is reconstructed using an analyzer downstream the sample. In combination with Bragg topography it allows obtaining high-resolution topographs and in contrast to conventional topography it additionally provides phase contrast.We apply this method to visualize the strain field around an indent in a thin Si wafer and in a compression Cu micropillar. Here we combine ptychographic topography with rocking curve imaging. This involves recording high-resolution topographs while rocking through a Bragg peak. Each pixel of the image records it own local rocking curve that is analysed in terms of integrated intensity, angular position and width.Ptychographic topography has the advantage that the sample is not scanned during ptychographic acquisitions, which renders the method compatible with in situ experiments. Furthermore, the technique relies on the use of a parallel beam, which ensures that, in contrast to Bragg projection ptychography, the illumination remains approximately constant during a rocking curve scan.

Nanocellulose has gained increasing attention as a composite filler, with a rising number of applications within biomedicine, coatings, membrane technology and smart materials.

The purpose of this work was to understand more about poly (vinyl alchohol)/nanocellulose composite film formation as well as film swelling.

Both crystalline nanocellulose (CNC) and TEMPO oxidized cellulose nanofibrils (TO-CNF) were used to prepare composites, with loadings up to 8 wt% in dry composite films.

Casting suspensions scattering profiles were investigated in order to elucidate the filler shape in PVA/nanocellulose suspensions, as well as the nature of the pure PVA suspension. Both dry films and suspension scattering profiles were investigated using general as well as shape specific models.

Furthermore, films were swollen in water, allowing the swelling process to be investigated with SAXS in situ. This allowed the monitoring of swelling dynamics. While PVA films redissolve completely, this was not the case for composites with 4 wt% loading of nanocellulose. This study allowed the investigation of the underlying swelling dynamics.

Low melting point metals (Ag, Au, Cu) deposited onto an amorphous dielectric substrate usually form three-dimensional islands (Volmer-Weber growth) before percolation. Stresses then develop in the compressive-tensile-compressive (CTC) sequence. We present a study of the stress and its relaxation in sputter-deposited Ag layers by periodic interruptions of the deposition. High-resolution curvature measurement provided access to quantitative stress values from the very beginning of deposition. In interrupted deposition, compressive stress has been developing during deposition while during pauses the stress reversed towards tension – all through the deposition. The interplay between these two observations – during deposition and in pauses – resulted in the similar overall CTC curve. It pointed to a phenomenon responsible for the tensile stress generation acting both during and after deposition. In addition, the interruptions resulted in the delay of percolation (in thickness terms) for the conditions explored, although those delays varied. The delay of percolation can be related to the reduction of the average deposition rate and to reduced supersaturation at the surface. However, other phenomena playing a role should be considered.

We report a versatile platform coupling nanocalorimetry with SEM, which allows imaging and electrical measurements of samples under different environments and can simultaneously measure the sample temperature and associated energy. This sensor consists of four independent heating/sensing elements for thermal measurements and eight electrodes for electrical measurements. All these are on a 250 µm x 250 µm suspended silicon nitride membrane. This membrane is highly electron transparent and mechanically robust enabling in situ SEM observation at different temperatures, environmental conditions, and pressures up to one atmosphere. We demonstrated that through membrane SEM high resolution imaging can be conducted at atmospheric pressures in a conventional SEM and was used to study in situ phase transitions in polymer film, charge transport in a nanowire in air and vacuum by EBIC. This versatile platform is applicable to materials research, nanotechnology, energy, catalysis and biomedical applications.

Ferroelectric materials are critical components in a wide range of devices such as non-volatile memories, actuators, sensors, and electro-optic devices. For the practical applications in recent trend of miniaturization, it is essential to understand and enhance ferroelectricity of thin films including piezoelectricity and polarization switching. Recently, special attention has been given to ferroelectric materials due to the presence of morphotropic phase boundaries (MPB), or strain driven mixed phases of ferroelectric domain that enhanced electromechanical property. In the ferroelectric BiFeO3 (BFO) thin films, for example, the film tends to form rhombohedral phase in the middle of tetragonal phase in order to relieve the stress from substrate. The existence of rhombohedral phase has been well predicted to enhance electromechanical properties of BFO thin films arising from the large lattice distortion under an applied electric field; however, its dynamic phenomena has not been clearly investigated yet partially due to the lack of experiment al tools.

Recently, time resolved micro X-ray diffraction under electric field allow us to resolve not only structural change but also electromechanical properties of thin films. Change of diffracted intensity and shift of diffracted peak position under electric field will provide information on ferroelectric switching and piezoelectric response, respectively. As results, we found nonlinear phase transition between simple cubic and super tetragonal structures. The simple cubic structure showed ferroelectric switching under electric field while supertetragonal only showed linear piezoelectric response indicating the origin of phase transition.

8:00 PM - TC02.11.08

Experimental Investigation on Structural Evolution of Amorphous Indium-Based Oxide Films During Annealing by In Situ XRD and EXAFS Measurements

Indium-based amorphous oxide semiconductors (AOS) have been used as the channel materials in thin-film transistors (TFTs) for display applications1,2). A typical AOS material is amorphous indium–gallium–zinc oxide (a-IGZO) with high Hall mobility of >10 cm2/Vs3). However, a-IGZO TFTs exhibit environmental-dependent instability, and the origin of such instability remains unkown4). Oxygen-deficiency related subgap states are considered to be the origin of the device instability. Here, we reported the post-annealing effect on the evolution of the local structure of metal-oxygen bonds for a-IGZO films using extended X-ray absorption fine structure (EXAFS) measurements, and investigated the effect of local structure evolution on the subgap states by the cathodoluminescence (CL) spectroscopy. We also used the in-situ X-ray diffraction pattern (XRD) to study the evolution of the long-range structure for a-IGZO film during annealing, and compared them with those of indium-gallium oxide (IGO) and indium-zinc oxides (IZO) to identify the influence of cation diffusion on the crystallization of a-IGZO films.Amorphous IGZO, IGO and IZO films were deposited on quartz substrates by DC magnetron sputtering, and the EXAFS and in-situ XRD measurements were performed at SAGA Light Source (Kyushu Synchrotron Light Research Center). CL measurements were done at 35 K.Increasing the post-annealing temperature makes to the cation-oxygen interatomic distances to approach those of the crystalline IGZO powder. The increase in the post-annealing temperature leads the Zn-O coordination numbers to change gradually toward the stoichiometric state, and the Ga-O coordination numbers to become larger than those of the crystalline IGZO powder, suggesting that the oxygen defects, such as the interstitial oxygen, may form in the local Ga-O structure. In contrast, the In-O coordination numbers almost kept constant at all annealing temperature. CL measurements show two types of deep subgap states near the middle of the bandgap, which are due to the effect of undercoordinated cation/oxygens. Moreover, we observed the crystallization behavior of amorphous IGZO, IZO and IGO films at different annealing temperatures to determine the activation energies for crystallization, and compared these activation energies to identify the influence of metal cation diffusion on the crystallization of a-IGZO film. These experimental observations open up a new route to understand the device instability of a-IGZO based TFTs.This work was supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (B) 16K21338 and for Scientific Research (C) 16K04966.[1] Junjun Jia, et al., Appl. Phys. Lett. 103, 013501 (2013).[2] Junjun Jia, et al., Appl. Phys. Lett. 106, 023502 (2015).[3] JunJun Jia, et al., Jpn. J. Appl. Phys. 55, 035504 (2016).[4] JunJun Jia, et al., Phys. Rev. Applied, Submitted.

The introduction of micro electro-mechanical system (MEMS) based heating holders for TEM has led to a renewed interest in in situ investigations of thermally activated processes in real time. The superior thermal stability of the MEMS-based heating holders, as compared to conventional furnace type heating holders, allows us to carry out controlled cooling and heating experiments on a wide variety of samples inside the TEM. Samples prepared for MEMS-based devices have a small thermal mass and are in direct contact with the micro-heater membrane. The temperature distribution across the micro-heater surface of the MEMS device depends on the design of the heating element, the location of the electron transparent sample window, and the thickness & composition of the membrane over and around the window. If overlooked, these factors could potentially result in large uncertainties in the data obtained from in situ heating experiments. Therefore, a reliable and easy approach to measure local temperature across a MEMS micro-heater in operando inside the TEM at high spatial resolutions is needed.Previous investigators have determined the temperature on a MEMS micro-heater device inside the TEM using; 1) electron energy loss spectroscopy data, 2) electron diffraction to quantify the thermal expansion of metal nanoparticles as a function of temperature, 3) filled carbon nanotube and β-Ga2O3 nanotube based ‘nanothermometer’ approaches, 4) temperature gradients from melting of metal islands and 5) infrared thermography to map the temperature of an active MEMS based heating holder placed inside a custom made vacuum station with an optical window. Here, we demonstrate an approach to measure the localized temperature on the micro-heater membrane surface inside a TEM that – 1) would overcome the issue of spatial resolution posed by thermal microscopy, 2) requires no additional detectors for gathering data via spectroscopy, 3) involves an easy sample preparation protocol, and 4) is compatible with any heater design. In this study, we carry out isothermal in situ heating experiments to determine the time required for sublimation of an isolated monodisperse polyvinyl pyrolidone (PVP) capped Ag-nanocube, inside the TEM. We then measure, the actual temperature of the membrane in contact with the nanocube by substituting the experimentally observed sublimation time into an analytical equation for sublimation time obtained by combining the Kelvin equation and kinetic gas equation. In addition, we also systematically evaluate the effects of electron beam heating on the sublimation by comparing sublimation times on full, partial and no exposure of PVP-capped Ag-nanocube to the electron beam.

Additive manufacturing of metal components involves fabrication of three-dimensional structures by melting small metallic particles using a raster-scanned laser beam in a layer-by-layer fashion. The process reduces the cost, time, skill barriers, supply chain, and manufacturing footprint required to fabricate highly customized components. Irregularities in the solidification conditions during laser powder bed fusion additive manufacturing (LPBFAM) processes can lead to localized defects, undesired phases, residual stress, compositional inhomogeneity, and poor quality of the final fabricated part. Here, we present in situ synchrotron x-ray radiography, x-ray diffraction, optical thermography and profilometry measurements of melt pool evolution, crystal phase, and layer-to-layer height variation during LPBFAM processing of a Ti-6Al-4V alloy. These combined techniques offer a multi-modal approach to elucidate transient behavior caused by the interaction among the melt pool, laser beam, and metal powder layers. We directly observe and quantify important process characteristics such as peak temperatures, temperature gradients, spatter ejection, melt pool oscillations, and liquid-solid phase transitions. An understanding of the dynamics of these events provides insights that enable microstructural control over the material present in the final part produced by LPBFAM. The formation of sub-surface porosity observed through time-resolved, in situ x-ray radiography is rationalized using hydrodynamic finite element simulations of Marangoni flow, vapor recoil forces and solid/liquid phase transformations. Our in situ diagnostic techniques allow detailed features in the final melt track morphology to be observed and associated with changes in thermal profiles. Along with providing process monitoring data to facilitate part qualification, data provided by our diagnostics can help validate process models. The practical implementation of incorporating these high-speed diagnostic techniques into commercial platforms is also discussed.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Work at the Ames Laboratory was supported by the Office of Energy Efficiency and Renewable under Contract No. DE-AC02-07CH11358. This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, CPA agreements 32035, 32037 & 32038.

For both fundamental and practical considerations, it is important to understand the intrinsic relationship between a material’s structure and its corresponding properties, both of which will govern the performance of the material. Despite the vast differences which exist in the molecular details amongst the various classes of polymers, such as thermosetting glassy resins and semi-crystalline thermoplastics, all polymers possess an ability to rearrange on a molecular level in response to thermal and mechanical forces. This paper investigates the effect that high pressure conditioning has on basic physical, mechanical, and structural properties of two classes of polymeric materials. Herein, we begin by presenting what effects pressure conditioning has on glassy networks with controlled molecular architecture that are synthesized with specific differences in crosslink density and backbone stiffness. One focus of this study will compare pressure conditioning to thermal annealing and thermal conditioning. The second part of the talk will cover the effect that high pressure has on the crystal/melt transitions as well as degree of crystallinity and alterations in crystal form in semi-crystalline thermoplastics. We investigate the influence of pressure on the resulting crystalline state. The pressure conditioning consisted of hydrostatically loading samples under controlled temperature and under controlled pressures in the range 130 – 190 MPa followed by a pressure soak. After pressure conditioning was complete, samples were stored at -40°C until subsequent testing. For the glassy networks, pressure conditioning was performed at temperatures below their glass transitions, and for the semi-crystalline thermoplastics, pressure conditioning involved crystallizing from the melt under pressure. Heating and cooling rates did not exceed 1°C/min. The glassy networks studied were aliphatic and aromatic crosslinked epoxies and all had glass transitions above room temperature. Sample characterization included compression tests and differential scanning calorimetry for the glassy networks and X-ray scattering and differential scanning calorimetry for the semi-crystalline thermoplastics. The measured mechanical, thermal, and structural properties were used to analyze the influence of the mechanical and thermal histories that were imposed on the samples and ultimately how these histories influenced the molecular structure.

8:00 PM - TC02.11.13

In Situ Characterization of Lithium Primary Batteries Using EIS and TXM

A rising interest in batteries has resulted from a need for improved energy storage systems for transportation and portable electronics applications. Lithium is of particular interest as an anode due to its low redox potential and high specific capacity. However, these systems have not been practically realized due to the nonuniform plating of lithium during charge steps. The resulting dendritic or mossy structures are a leading cause of failure for these batteries [1]. As such, the commercial use of Li anodes has been largely limited to primary cells, batteries designed to be discharged just once. The cathode in these commercial cells is traditionally selected as MnO2 due to its low cost and ability to intercalate Li.

Recent advances in in situ electrochemical transmission X-ray microscopy (TXM), with its ability to provide spatial information alongside electrochemical characteristics, enable exploration of the underlying physics of electrochemical reactions that occur at the surfaces and inside energy storage systems [2]. In this work, we use primary Li coin cells as a basis for understanding changes in the electrodes during cycling. Specifically, we discharge cells at a range of C rates to specified states of charge (SOC). At each SOC for a cell, electrochemical impedance spectroscopy and TXM are employed in order to provide electrochemical and structural information about our cell. The same methods are subsequently used for cells that have been discharged and charged for a range of cycles within specified capacity windows. In this way, we correlate three-dimensional morphological and microstructural changes within the electrodes to electrochemical parameters and failure mechanisms caused by battery operation.

Flammability performance of polymer-flame retardant blocks was evaluated by subjecting the samples to European Union glow-wire test [1]. Two categories of blocks were tested. The first block set consisted of conventional extruded polymer test bars comprising a homogenous blend of flame retardant and high impact polystyrene. Different weight percent of flame retardant was used including 3 wt% and 12 wt%. The 12 wt% had passed previous UL 94 test [2], the 3 wt% failed.

The second block set was 3D printed test bars prepared using a dual filament printer with the fused deposition modeling technique. The bars were designed as (a) 100% flame retardant/ABS filament, (b) a 1:1 layered structure of flame retardant/ABS and ABS filaments, and (c) a 1:3 layered structure of flame retardant/ABS and ABS filaments. The aim was to determine which structures which efficiently use flame retardants in near-surface layers, with a pure polymer surface layer for wear and durability by taking advantage of the control of material placement that additive manufacturing affords.

A glow-wire instrument was designed to fit into the CAMD tomography/interferometry beamline.A number of heating cycles were carried out with stepped-grating 2D X-ray interferometry [3,4] imaging performed in-between. These images provide details on sample transformation with heating. Post-heating, samples were selected for interferometry/tomography.

Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed C70 peapods, which most likely can be identified with a fully sp3-bonded monoclinic structure, here named V carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near K-edge spectroscopy and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ~400 GPa, which well explains the “ring crack” left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp3-hybridized carbon structures by using fullerene@nanotubes carbon precursor as building blocks containing odd-numbered rings.

8:30 AM - *TC02.12.02

Effects of Simultaneous Pressure and Temperature on the Stability of Si24

A new phase of silicon with composition Si24 and a clathrate structure has recently been synthesized by methods of high-pressure chemistry. There is evidence that it nearly has a direct band gap [1], and temperature and pressure allow tuning of the electronic properties of Si24. Exploring the effects of temperature and pressure on its thermodynamics is of fundamental interest, too, and is the focus of this research.

Using diamond anvil cells with temperature control, we measured Raman spectra of Si24 at combinations of temperatures and pressures. The shifts of the Raman peaks, Δω, were fit to functions of the form

Δω = A P + B T + C P2 + D PT

where P and T are pressure and temperature. The first two terms, proportional to P and T, are the well-known quasiharmonic and anharmonic phonon shifts, typically measured at low T or P, respectively. We were surprised to find that the largest contribution to Δω for a bending mode of B3g symmetry was the fourth term, the cross term in PT, even though the temperature range was only 320 K and the pressure range was 8 GPa [2].

Most of the entropy of Si24 originates with atom vibrations, so the influence of this cross term in PT on phonon frequencies may be important to the entropy of the material. Such effects have been noted in the geophysics literature, although their origin is largely unexplored. One approach involves how the anharmonic behavior with T is altered by P. Alternatively, the quasiharmonic behavior with P is altered by T. These two explanations must be equivalent by a Maxwell relationship.

The talk will include discussion of an emerging effort to use inelastic neutron scattering to measure phonon spectra on materials under pressure. The simultaneous effects of T and P, not understandable from either T or P alone, offer rich opportunities for experimental and computational research.

[1] Nature Mater. 14, 169 (2015).[2] PRB 95, 094306 (2017).

9:00 AM - TC02.12.03

Coupling between the Electrical Conductivity and Nanocrystalline Structures in a Single Nanowire under High Pressure

The electrical transport measurements under high pressure (HP) in a diamond-anvil-cell (DAC) are expanding the domain of versatile measurements following the emerging techniques. Focused ion beam-induced deposition (FIBID) is one of the one-step maskless processes to fabricate the pre-patterned electrical contacts or nanostructures by local deposition of metal (Platinum (Pt) or Tungsten (W)) to attach the samples electrically and mechanically inside a DAC. The applicability of such HP experiments is restricted by the common drawbacks: (a) the electrical Pt/W leads break down under HP and widen with plastic flow and (b) their mechanical stability is governed by the high carbon percentage in the deposits due to the decomposition of the organometallic precursor gases [(CH3)3CH3C5H4Pt] during deposition. Due to strong correlation between the electronic and structural properties, FIBID nanowires appear either metallic or semiconducting depending on their compositional variation (metal and amorphous carbon (a-C) ratio). The transport properties are highly sensitive to their structural deformations too. We observed a structural transition in our FIBID NW accompanied by a semiconductor-metal transition (SMT) above the percolation threshold pressure of Pth ≈2.9 GPa at 300 K. Analysis of the current-voltage (I-V) characteristics revealed the presence of zero-bias differential conduction humps across Pth due to a quantum tunnelling conduction process assisted by the percolation. We defined a quantum-tunnelling boundary (QTB) at a pressure beyond Pth where the band-gap sharply decreased and confirmed the metallic conduction. We presented a quasi-ballistic formalism of the electrical transport to explain the tunnelling mechanism inside such compressed nanowire. Moreover, the cross-sectional TEM analysis of the deposited nanowire revealed the presence of Pt nanograins appeared as Pt-quantum dots (QDs) in the a-C matrix. Hence, we expected the electron-electron interactions with the quantum-interference effect by strong electron confinement in the QDs. Again, the external pressure modified the distances between QDs resulting the significant variations in the electrical transport mechanisms. To explain the elctrical conductivity phenomena under HP, we performed a fast computational methodology (Voronoi diagram) by analyzing the spatial distribution of QDs in the recovered samples at different pressures. Our results indicated that FIBID Pt-C nano-structures were highly susceptible to their metal and carbon concentration and distribution, the extent of disorder (Ga+ ions), diameter and temperature etc. We conclude that it is very important to study such nanowires individually before using them for other HP experiments. Our results are very new and never been reported elsewhere.

Abstract Body: TiZrNi alloys exhibit periodic, quasi-periodic and glassy structures depends on their cooling rates. The semi-rapid quenched alloys form quasicrystals and the formation and stability of quasi-periodic materials have been refocused after the awarding of Nobel Prize of Chemistry in 2011 to Dr. Shechtman for the discovery of quasicrystals. Ti/Zr-based quasicrystals are the second largest family forming stable quasicrystal followed by Al-based ones. One of the most interesting structural properties of Ti/Zr-based quasicrystals is that they absorb a large amount of hydrogen exceeding the density of liquid hydrogen. In fact, Ti53Zr27Ni20 quasicrystals are known to absorb near 2.0 wt. %. hydrogen, reversibly. Further, theoretical calculation and modeling of their approximant phases predict that a significant amount of interstitial sites are still available for hosting hydrogen suggesting the materials have technical advantages for hydrogen storage application.To realize the prediction, we pressurized TiZrNi alloys including C14 Laves phase and quasicrystals using a diamond anvil cell up to 48 GPa under hydrogen environment and estimated the hydrogen loading capacity and transport properties. By analyzing the peak shifts in synchrotron-based X-ray diffraction data revealed that quasicrystal phase sustained to the applied pressure with uniform shift of the main peaks suggesting that hydrogen atoms diffuse into the interstitial sites homogeneously without phase transformation. The maximum value of hydrogen loading at 48 GPa was near 4 wt. % with a completely reversible process. The hydrogenated samples showed in an order of 10 times greater decreasing of electrical conductivity values as increasing pressure than the pristine ones. Mechanism of hydrogen loading, effects of hydrogen on structural stability and transport properties as a function of pressure will be presented.

A3BX4-type compounds, such as Ag3PO4 and Na3VO4, have aroused increasing research interests in solar energy conversion and storage, environmental remediation, and solid electrolyte applications, which can be ascribed to their ease of synthesis, stable structure, narrow band gap, high photocatalysis activity, and excellent ionic conductivity. To date, the phase transition and electrical/ionic conductivities of this type compounds at different temperatures have been extensively investigated. Here, the pressure-induced structural evolution of several A3BX4-type compounds was studied by in situ synchrotron X-ray diffraction and Raman spectroscopy experiments. For Ag3PO4, the phase transition started from ~2 GPa and was reversible during compression up to 50 GPa and decompression to ambient conditions. The optical and electronic properties were also investigated using in situ high-pressure UV-vis spectroscopy and in situ high-pressure electrical measurements. Furthermore, the pressure-dependent optoelectronic properties were interpreted in terms of crystal structure combined with theoretical calculations.

Novel ferritic superalloys based on the Fe-Al-Cr-Ni-X (X = Ti, Hf, Ta, and Zr) systems has been developed for the application of ultra-supercritical fossil-energy (FE) power plants under the condiction of the steam temperature of 760 oC and the pressure of 35 MPa, in order to improve the efficiency of plants and reduce the greenhouse gases emission. In this project, the bulk thermodynamic properties (the formation and ordering energies) and interfacial energies, including anisotropic effects, and elastic constants (Cij) in the system of the body-centered-cubic (bcc) iron, and relevant B2 and L21 intermetallics, are calculated and determined by first-principles calculations. Besides, advanced microstructural characterization tools (e.g., the high-resolution analytical-electron microscopy, local-electrode-atom probe, high-resolution electron microscopy, laboratory and synchrotron x-ray diffraction, neutron diffraction, and ultra-small angle X-ray scattering) and mechanical tests (e.g., compression, tension, and creep) coupled with in-situ neutron diffraction, are conducted for the validation of the calculated results. Dislocation-dynamics simulations, which incorporates the data of the first-principles calculations and experimental results, are developed to guide the alloy design with optimal microstructural parameters (e.g., the precipitate size, morphology, volume fraction, and lattice mismatch) to improve the creep resistance of ferritic superalloys for applications in FE power plants. With all these results, we are able to develop and integrate modern computational tools and algorithms to design high-temperature alloys for applications in FE power plants, and to understand the processing-microstructure-property-performance links underlying the creep behavior of novel ferritic alloys strengthened by hierarchical coherent B2/L21 precipitates.

11:00 AM - TC02.13.02

Metals under High-Pressure, High Temperature or During Plastic Deformation—In Situ Studies of Thermo-Mechanical Response by Neutron and Synchrotron Quantum Beams

In-situ neutron and synchrotron X-ray diffraction deliver unique and complementary insight into the microstructural evolution of metals at high temperature, during thermo- mechanical processing or under high pressure. Neutrons illuminate a larger bulk volume and reveal quantitative phase abundance, bulk texture, lattice parameter changes and other ensemble averaged quantities. They are particularly sensitive to characterize atomic order and disorder in titanium aluminides. In contrast, fine- bundled synchrotron high-energy X-rays deliver reflections from a number of individual grains. For each constituting phase, their statistics and behavior in time reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, twinning, etc. Grain orientation correlation can be revealed and lattice strain gives complementary insight to the transformation and reaction processes. This presentation reviews pioneering experiments on metallic and intermetallic systems in reciprocal space, which nowadays serve the wider community.

11:15 AM - TC02.13.03

Study of Microstructure Evolution and Mechanical Properties by an In Situ Neutron Approach on NbTaTiV Refractory High-Entropy Alloys

Different from conventional alloys, high-entropy alloys (HEAs) have multiple principal elements, often five or more. Carefully-designed HEAs tend to form solid solutions with simple structures based on multiple principal elements. This trend results from the fact that the high mixing entropy enhances the formation of simple solid-solution phases, such as the face-centered-cubic (FCC), body-centered-cubic (BCC), and hexagonal-close-packed (HCP) structures. Due to the microstructural stability at high temperatures, HEAs are frequently considered as potential structural materials for elevated-temperature applications. The focus puts on the design and development of HEAs containing single solid-solution phases through the integration of theoretical modeling and experimental demonstration. In this study, we attempt to develop the refractory high-entropy alloys, which contain the single BCC solid-solution phase. NbTaTiV refractory HEAs were designed by the CALculation of PHAse Diagrams (CALPHAD) approach and investigated using the neutron diffraction (ND), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and atom probe tomography (APT). The as-casted NbTaTiV refractory high-entropy alloys exhibit the conventional dendritic structure. The systematic heat-treatment has been performed to study the microstructure evolution. The heat treatment leads to a gradual transition from the dendritic to single BCC solid-solution phase structure, as clearly revealed by APT. The solid-solution strengthening effect, which derives from the severe lattice-distortion, is optimized by the homogenization treatment. Thus HEAs exhibit high yield strengths at room as well as elevated temperatures. The lattice-distortion has been quantitatively calculated by the lattice distortion factor of . The determined parameter, considering experimentally-measured values, was well matched to the theoretically-calculated parameter, which is obtained from first-principles calculations. Moreover, the comparison of in-situ neutron diffraction studies between as-cast and homogenization-treated alloys has been conducted to demonstrate the effects on elastic and plastic deformation behaviors by solid solution strengthening, which is induced by lattice distortions.

In electrochemical energy storage and conversion, electrodes and electrolytes are the key components of batteries, fuel cells and capacitors. Electrons and ions are the relevant electric charge carriers. The key player in technology for the hydrogen economy is the proton - an elusive charge carrier which cannot be so easy detected 1. Ceramic proton conductors can be used as electrolyte membranes in solid state devices. Smart defect engineering makes that oxygen vacancies can be filled with oxygen ions from ambient vapor water molecules. The protons from the water molecule form intermediate OH bonds with proximate oxygen ions. Upon thermal activation, the OH bonds melt and the proton be-comes liberated as positive charge carrier. The transport properties of the yttrium doped barium cerate and barium zirconate electrolytes were investigated by thermodynamic parameterization of their structure with temperature 273 K - 773 K and pressure 0 - 6 GPa. The proton conductivity activation energy decreases linear with increasing lattice spacing, suggesting that epitaxial strained films should be promising future electrolyte membranes 2, 3, 4. The Raman modes increase with increasing pressure and get a slightly higher "pitch" upon protonation 5. The OH bond breaking occurs at a characteristic temperature range which is accompanied by the onset of a lateral proton diffusivity which accounts for the macroscopic conductivity as measured with electroanalytical methods 6. At the microscopic scale, ambient pressure XPS and quasi elastic neutron scattering which were carried out operando parallel on the same samples with impedance spectroscopy 7, confirm that it is exactly this proton phonon coupling which switches the proton conductivity on. The quantitative analysis of the proton jumping frequencies showed that the Ce-O stretching mode is the effective propeller for the proton at work. Moreover, the temperature dependence of the proton jump frequency follows exactly the mathematical model for a Holstein polaron 8, rendering the proton conductivity process in ceramic proton conductors a genuine proton polaron 9.

Electrochemical reactions of energy storage and conversion electrode materials are generally complex multistep mechanisms that may be composed of both electron transfer and chemical steps. However, this underlying complexity is generally obscured into a simplified current voltage curve describing the global reactions. Deciphering the electrochemical responses has thus relied on the measurement of structural, chemical, and electronic properties of materials ex-situ, both pre and post electrochemical testing, and trying to use these properties as predictive descriptors of material performance. Although this approach has been useful in limited cases, it is well known that during operation, the materials often take on very different properties than those measured during their equilibrium resting states. Thus, the development of accurate descriptive theories of materials for electrochemical energy storage and conversion necessitates the development of techniques that allow for the study of these materials during operation.Scanning transmission x-ray microscopy (STXM) combines the chemical selectivity and electronic information of soft x-ray absorption spectroscopy with high resolution microscopy, allowing for spatially resolved spectroscopy of individual particles. We have developed platforms to extend this technique to the in-situ monitoring of battery electrodes and fuel cell electrocatalysts through mapping of bulk electronic states during operation. In this talk I will present recent insights we have gained through operando electrochemical STXM applied to lithium insertion kinetics in lithium iron phosphate olivine battery electrodes and bulk electronic states of cobalt hydroxide electrocatalysts during the alkaline oxygen evolution reaction.

The search for high-rate energy storage materials that can deliver high power on discharge and rapid charging times has been primarily focused on nanoscaling and nanostructuring known battery materials such as TiO2, Nb2O5, and Li4Ti5O12. Recently, we discovered and reported high-rate performance in bulk electrodes of the bronze-like phase T-Nb2O5[1] and the crystallographic shear structure TiNb24O62[2]. With micrometer-scale particles, thick electrodes, and the absence of carbon-coating or any synthetic or post-synthetic treatment, capacities of 120 mA×h×g–1 were realized at high current densities corresponding to discharge and charge in a matter of minutes as opposed to hours for conventional materials.

Herein, we have undertaken a mechanistic study to understand how these bulk, insulating oxides are able to withstand rates of 10C to 20C (3 to 6 minutes charge/discharge) over length-scales that are one to two orders-of-magnitude larger than most high-rate battery material candidates. Advanced characterization techniques are employed, particularly operando synchrotron X-ray diffraction and X-ray absorption spectroscopy. The diffraction experiments are particularly demanding as the structures have large units cells, superstructure, and site disorder; additionally, collection at high-rate required a state-of-the-art in situ electrochemical cell and an area detector to collect diffraction patterns every few seconds. Whilst diffraction offered insights into the long-range structure and lattice changes, extended X-ray absorption fine structure (EXAFS) provideed local atomic information and X-ray absorption near-edge spectroscopy (XANES) revealed changes in atomic structure and coordination geometry at the transition metal sites. The electronic structure changes are particularly important in mixed-metal oxides such as the Ti–Nb–O and Nb–W–O systems that will be described here to understand the stages of the redox process and the nature of excess capacity beyond one electron per transition metal observed in these promising systems. In situ/operando techniques provided critical insight into the energy storage mechanisms of these complex functional oxides.

Recent research has made it clear that a proper understanding of energy storage materials requires experiments that probe the system while it is actively charging/discharging. Layered transition-metal oxide materials are of primary commercial interest due to their high theoretical storage capacity. Operating closer to these limits will enable more efficient and powerful energy storage solutions, but requires a more complete understanding of the reaction mechanism. Combining transmission X-ray microscopy and X-ray spectroscopy enables the mapping of chemical oxidation states with sub-micron resolution. Using this approach, we have explored the transformations occurring in several nickel-based layered cathode materials while under operating conditions. This has revealed chemical inhomogeneities within secondary particles at intermediate states of charge. Additionally, the storage atmosphere affects the sub-micron behavior. The formation of a lithium carbonate layer upon exposure to ambient water vapor has a dramatic impact on the reaction kinetics. Bulk diffraction indicates a two-phase reaction: spectro-microscopy reveals a staggered, rapid transformation occurring at the secondary particle level.

2:45 PM - TC02.14.05

Local Structural Fingerprint for Tracking Li-Ion Intercalation in Zero-Strain Lithium Titanate from In Situ X-Ray Absorption Spectroscopy and First-Principles Calculations

Zero-strain electrodes are appealing for battery applications due to their extraordinary cycling stability as a result of the negligible volume change while they are discharged/charged repeatedly. On the other hand, this same property makes it challenging to probe structural changes in electrodes during the operation of batteries, which obstructs fundamental understanding of their electrochemical processes. A classic example is spinel lithium titanate (Li4/3Ti5/3O4), wherein Li intercalation and the related phase transformations have been the subject of intense debate. Herein, in-situ X-ray absorption spectroscopy in combination with ab initio calculations was applied to studies of Li intercalation in Li4/3Ti5/3O4. Based on the excellent agreement between the computational and experimental spectra, we identified the origin of the main features in the near-edge fine structures of Ti K-edge in terms of local atomic arrangements and chemical bonding in lithium titanate. In particular, we found that the area of the predominant pre-edge peak is proportional to the local distortion of TiO6 octahedra, which varies with the amount of the intercalated Li. Thus, the pre-edge peak was used as a spectral fingerprint for quantitative assessment of phase evolution in lithium titanate during lithiation. Results from this study revealed that the solid solution was involved over a wide range of the Li concentration. Such a complicated kinetic pathway contradicts the general belief of Li intercalation via the macroscopic two-phase transformation. The established spectral fingerprint may be broadly applicable to tracking kinetic pathways of Li intercalation in various electrode materials.

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BREAK

3:30 PM -

OPEN DISCUSSION

3:45 PM - TC02.14.07

In Situ Investigation into the Effects of Processing Conditions on Cation Mixing and Performance of an NMC 111 Cathode Material

Research on lithium ion batteries has quickly expanded in recent years due in large part to the prospect of their use in electric vehicles and household energy storage solutions. Efforts to improve lithium ion battery performance have typically focussed primarily on improving the cathode material, as it is the limiting factor in terms of capacity and overall battery lifetime. In particular, LiNi1/3Mn1/3Co1/3O2 (often referred to as NMC 111) is becoming a material of focus for commercial production. A significant challenge in synthesizing this material is the propensity for Ni/Li cation mixing in the octahedral sites. While several studies have been conducted correlating synthetic and processing methods to the observed levels of cation mixing and electrochemical performance of the final material, so far none of these studies have probed in-depth the cation mixing phenomenon in situ on a mechanistic level. Thus, presented herein is a detailed investigation into the processing conditions (e.g., thermal and compositional) for NMC 111 beginning with a pre-lithiated precursor material. Through in situ, variable temperature XRD methods, the relationship between cation mixing, sintering temperature and time, as well as potential methods for its reversal, were investigated. The importance of this knowledge in the determination of ideal processing conditions for NMC 111 (and by extension, cathode materials in general) is further demonstrated through a final analysis of the quality of Li+ distribution in these materials as assessed by microscopy techniques and electrochemical coin cell tests.

In situ probing of liquid-solid-gas interfaces with powerful electron spectroscopies and microscopies is a current trend in modern catalysis, electrochemistry and biomedical research. The key parameter determining the analytical power of these methods is an electron mean free path in the probed media. The high energy of the electrons in (HR)TEM allow imaging the objects immersed in submicron thick liquid layers with unprecedented resolution but fall short in the precision of analysis of interfacial electronic structure. On the contrary, judiciously designed differentially pumped electron optics and sample delivery systems in high-pressure x-ray photoelectron spectroscopy enable atomic layer sensitivity but truly ambient pressure has not been achieved yet.Recently, we propose to use atomically thin graphene as electron transparent and yet molecularly impermeable membranes for separation of the liquid sample from the high-vacuum of the spectrometer or electron beam optics. This enables to apply low electron energy surface sensitive spectroscopic and imaging techniques such as XPS, XAS and SEM to perform measurements liquids and atmospheric pressure gases.Developing this line of research, we report here on our recent tests of atmospheric pressure PEEM setup to characterize the electrochemical interfaces with mesoscopic spatial resolution. Using model electrolytes, we image and spectroscopically (XAS, AES) discriminate between different electrochemical phenomena at working electrode-electrolyte interface. Polarization, specific adsorption as well as plating/stripping reactions have been monitored in situ during cycling of the electrochemical cell.The design of the graphene liquid cells enables an application of the effective image recognition and Big Data processing algorithms to interpret PEEM hyperspectral datasets. The limiting factors and artifacts such as radiolysis will be discussed.

The fuel cell technology may not become commercially viable unless affordable, highly active and durable nanocatalysts for speeding up the sluggish chemical reactions driving cells’ operation, such as the oxygen reduction reaction (ORR), are developed. Indeed, a number of excellent nanocatalysts for ORR, for the most part metallic nanoparticles, were developed recently. Despite real progress, fuel cells are not yet on the market. That is so, mostly, because metallic nanocatalysts proven excellent in a Lab, i.e. ex situ, do not necessarily deliver the expected high performance inside operating fuel cells. The underperformance reflects the fact that under actual operating conditions, metallic nanocatalysts undergo particular atomic-level changes, ranging from order-disorder transitions and gradual growth to nanophase segregation and even complete disintegration, and so suffer a substantial loss in ORR activity. To be successful, efforts to limit the latter through taking control over the former need precise knowledge of the concurrent evolution of the chemical composition, phase state, 3D atomic structure and ORR activity of the nanocatalysts that takes place while they function inside fuel cells. We will present results from recent in-operando energy dispersive x-ray spectroscopy and atomic pair distribution studies on binary and ternary noble (Pt, Pd)-transition metal (Ni, Co, Cu, Sn) nanoparticles used as ORR catalysts at the cathode of an operating proton exchange membrane fuel cell. Also, we will show examples how the knowledge obtained helps bring fuel cells a step closer to commercialization.

Computational driven design of materials has provided guidelines for precisely synthesizing novel materials with desired properties. However, the current approaches are limited when predicting the phases that can be accessed along synthesis pathways, especially the intermediate/metastable phases. To overcome this limitation, we developed an approach that combines in-situ X-ray characterization and theoretical models to investigate the nature of reaction pathways via hydrothermal synthesis. Our hydrothermal reactor was adapted from previously established reactor designs [1], but with both ends of the glass reactor flame sealed to mimic a conventional autoclave. Additionally, the experimental reaction conditions investigated in this study were guided by thermodynamic calculations that were developed by our theory collaborators, as published in Ref. [2,3].

Here, the MnOx system is utilized as a prototype system due to its rich polymorphism, which provides us with many possible reaction pathways to explore. We monitor the hydrothermal synthesis of MnOx in real-time with in-situ wide-angle X-ray scattering (WAXS) at 160 oC for 24 hr. The influence of [K+] on the reaction pathway was studied, with a fixed [MnO4-] and pH value. The study shows the presence of an intermediate phase during the transition from MnO4-(aq) to MnO2(s). By varying the [K+], the stability of the intermediate phase can be tuned. The structure of the intermediate phase and overall formation pathways are consistent with our theoretical predictions. In the course of this research, the experimental inputs are used to further refine the theory, which leads to precisely pinpointing the synthesis conditions for specific polymorphs. Overall, this study successfully demonstrates how experiment and theory work together to develop sophisticated modeling for predicting reaction pathways. In particular, the in-situ X-ray characterization has irreplaceable significance in investigating pathways/intermediates in real-time. The future outlook for this “synthesis by design” approach is promising for other binary and ternary oxides with high polymorphism.

The understanding of the detailed nanostructure and surface sites of Pt (or Pd) based nanoalloy catalysts is of great significance for advancing the design of low-cost, active and stable catalysts for catalytic oxidation of hydrocarbons. This understanding is also important for the fields of heterogeneous catalysis, emission control, and sustainable energy production and conversion. However, one of the key challenges is the ability to determine the surface active sites and intermediate species of the catalysts in correlation with the nanostructure during the catalytic reactions. In this report, we will discuss recent findings of an investigation of Pd or Pt based binary and ternary nanoalloy catalysts for low temperature catalytic oxidation of hydrocarbons. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTs) and/or Synchrotron High-Energy X-ray Diffraction techniques will be employed for the characterizations. One example involves propane oxidation under controlled reaction conditions. Results on a structure-composition-activity correlation will be discussed, which shed light on the design strategies of advanced catalysts.

Thanks to the advanced in situ techniques, we have chances to observe the formation and transformation of materials directly, and to find out new phenomena in crystallization.We have attempted to regulate the structure of materials by controlling the diffusion and reaction rates of chemicals. By adjusting the diffusion and reaction rates, different shapes of calcium carbonates were synthesized [1-2]. Under a condition of quick reaction and diffusion limitation, snowflake-like calcium carbonate particles were synthesized for the first time [1]. By changing the diffusion of reactive ions, platinum particles switch from polyhedral shapes to porous dendritic spheres [3]. In the synthesis of silver particles, silver dendrites were largely formed in a diffusion limitation, which is independent on the preparation methods [4-7].By the real-time laser holographic interferometry, we found that the chemical concentration gradient on the front of growth surface was accompanied with the formation of dendritic structures. A change of concentration gradient leads to a change of dendritic structures. Phase field simulation confirmed the role of chemical concentration gradient on the development of dendritic structures. The surrounding effect was extended to temperature, in which a temperature gradient on the growth front of crystals also led to the formation of dendritic structures. Therefore, the local surrounding plays a dominant role on the structure development of materials. By a designed in situ SEM, the online formation and transformation of material structures at various surroundings is disclosed, which lightens us to understand the formation mechanism of snowflakes, as well as the diversity and complexity of materials structures.

Environmental Transmission Electron Microscopy (ETEM) is a powerful technique to observe the formation and evolution of materials in real time under reaction conditions, and thus offers opportunities to enhance our understanding of complex physical and chemical processes at the nano- to atomic scale. The development of new direct electron detectors has lead to significantly improved detective quantum efficiencies over CCD cameras. In the Fall of 2013, we installed the first Gatan K2-IS direct electron detector at the Center for Functional Nanomaterials (CFN) at Brookhaven National Laboratory. This detector streams images at 1920 x 1792 pixels at 400 frames per second, resulting in a tremendous data rate of approximately 3GB/s. This data rate compels the development of automatic image analysis algorithms to handle the torrent of data in order to extract quantitative information that can be mined via sophisticated statistical analysis methods to help understand underlying physical phenomena.

We have developed a complete pipeline for the automatic detection and tracking of the nanoparticles over time. We have chosen two separate physical systems to study. The first system is the sintering and Ostwald ripening of Au nanoparticles on SiN substrates: this system is relevant to understanding the fundamentals of nanowire nucleation and growth and provides very high feature contrast, simplifying the image analysis. The second is the conversion of FeOx nanoparticles on TixOy substrates to metallic Fe in a reducing environment: this system is relevant to nanotube nucleation and growth and provides very weak feature contrast, resulting in a significantly more challenging image analysis problem.

We have created a Python-based code that allows computation on multiple nodes of the high performance computing cluster and installed a direct connection (at 10Gb/s) from the CFN to Brookhaven’s institutional computing cluster. The combination of high-speed data transfer and parallel computing is expected to lead to near-real time image analysis, greatly facilitating our ability to extract meaningful statistical data. We anticipate presenting results that demonstrate this real-time analysis at the meeting, as well as comparisons with computational simulations of these processes.

Materials functionality is strongly dictated by structure and organization and understanding how structures are formed, through crystallization and nucleation, will be a critical tool for designing materials with distinct applications. Specifically, in the agricultural industry, thiamethoxam (TMX) is an organic solid that functions as an insecticide, but because of high water solubility tends to ripen into large crystals and consequently sediment in colloidal suspensions. It would therefore be valuable to gain a superior understanding of the crystallization and nucleation process. However, crystallization and nucleation of organic compounds has been challenging to visualize because they are typically not highly conductive, thereby susceptible to charging, and / or need to be immobilized on surfaces. The process of crystallization and nucleation is driven by molecular solvent and intermolecular interactions and this cannot be observed when immobilized or coated. To elucidate the full range of interactions that drives these processes, organics must be directly observed in-situ within their native, liquid environments.

In this work, we developed an in-situ approach to visualize crystallization and nucleation of organic materials by utilizing a liquid cell with Helium Ion Microscopy (HIM). Previously, in-situ imaging has been done by utilizing liquid cells with electron microscopy techniques, but visualizing organic materials with these methods is problematic because of charging and excessive specimen damage. HIM is a well-suited method to image unaltered organic materials with minimal charging, provided by sufficient charge compensation via an incident electron flood gun, and minimal specimen damage. Here we demonstrate the use of in-situ liquid cell capabilities on the HIM, to initiate and directly imaging thiamethoxam nucleation and crystallization in an aqueous environment. We investigate the crystallization and growth processes as a function of ion dose and acceleration energy. This information will help guide our understanding of crystallization in organics and facilitate improvements to TMX functionality. Future plans to introduce high binding-affinity phages into the solution to study changes in crystallization and incorporate flow inlets and outlets allowing for interchangeable environments to elucidate a range of interactions that effects TMX crystallite structure and organization will also be discussed.

In comparison to other material classes, dislocations have a unique role in semiconductors. They have a significant impact on charge carrier dynamics, in addition to being agents of plasticity, thereby leading to a coupling between electronic and mechanical properties. A technologically important manifestation of this coupling is in the form of carrier recombination-enhanced dislocation motion (REDM) – reported on previously as a failure mode in GaAs based optoelectronic devices.1 Our understanding of this process is still limited, not least due to the difficulty of observing such processes. In this study we used electron channeling contrast imaging (ECCI) to study e-beam induced REDM in GaAs on silicon substrates that are being used for low threshold, high power quantum dot lasers.2 ECCI provides an unprecedented view of dislocations in as-grown films with minimal artifacts of the type that arise during conventional TEM sample-preparation, and hence is more representative of conditions in optoelectronics devices compared to TEM based investigations reported on previously.3 The driving force for dislocation motion upon e-beam excitation was residual strain in the GaAs/Si stack, which resulted from thermal expansion mismatch upon cooling after growth. We will present results on the dynamics of a number of REDM processes involving dislocation glide, dissociation into partials, cross-slip etc. These observations have been made at several temperatures through the use of a temperature-controlled stage; this offers insights into the energetics and time-scales of these processes for the first time in such heterostructures. We believe that a clearer understanding of defect evolution will enable more reliable heterogeneously integrated III-V/Si laser diodes and other active devices.

Determining the in situ surface structure and composition of nanostructured, multimetallic catalysts is critical for understanding their chemical properties. The surface structure of a particular region of the material depends on the temperature and the local partial pressure of the reacting gases. This local pressure can vary due to the nanoscale flow through the material. Here, we combine experimental characterization of the morphology with several types of computation to study the spatially resolved surface structure and composition of nanoporous gold, a silver-gold bimetallic alloy, in reaction conditions.

First, field-ion beam scanning electron microscopy was used to obtain an accurate, experimental morphology of a nanoporous gold sample. Next, lattice Boltzmann fluid dynamic simulations were performed to simulate the nanoscale flow through this morphology under catalytic reaction conditions. These results were then used as input for a thermodynamic model based on first-principles calculations. This allows a realistic prediction of the local surface structure at each point across the entire material, accounting for the temperature and local pressure. These results show that much of the material remains catalytically inactive due to low local O2 pressures, since low O2 pressures result in pure gold surfaces that are too inert to be catalytically active. Our results also predict that AgAu catalysts should have a peak in activity at a moderate temperature, while pure Ag and Au catalysts should not, in agreement with experimental results.

The sub-atomically focused e-beam of an aberration corrected electron microscope offers a unique opportunity to manipulate and control matter on the atomic scale, including vacancy formation and migration, formation and breaking of chemical bonds, and adatom dynamics. Combined with real time imaging and spectroscopic capabilities, this provides a unique platform to study chemical reactions and transformations in real space. Here, we explore the pathways towards controlling and manipulating the surface chemistry of graphene carbons to establish beam-induced transformation pathways, the interplay between thermal and beam effects. In particular, we explored the effects of rapid vacuum annealing, migration and interaction of defects at elevated temperatures, and explored beam-induced control of point defects. We further demonstrate that beam path can be a significant control variable. Finally, we demonstrate that the combination of beam-induced organic reactions and beam control opens the pathway for manufacturing of atomically-defined structures, including multilayer graphene, and the incorporation of dopant atoms in the graphene lattice.

This research was conducted at and partially supported SVK the Center for Nanophase Materials Sciences, which is a US DOE Office of Science User Facility. Research for OD, SJ was sponsored by Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy. A.M. acknowledges fellowship support from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.

Electrical annealing of metals can create a very complex thermo-mechanical field in the specimen due to the motion of atoms under the electron wind. The high temperature and accompanying electron wind enhance grain boundary mobility and the grains increase in size to reduce the total energy. Our hypothesis is that externally applied current density induces secondary thermal (Joule heating) and mechanical fields and their overall effects are synergistic (and not additive) to change the microstructures. To prove this, we carry out in-situ EBSD (SEM) experiment on Zircaloy-4 samples. In this study, we have developed jet-polishing recipes to prepare high quality specimens for EBSD. After sample preparation, they are bonded suspendedly on MEMS devices with their two ends connected to two electrodes. The MEMS device is accommodated in a custom-designed SEM holder with biasing capability. Our preliminary experimental results on Zircaloy-4 show appreciable microstructure and texture change. The average grain size increased from original 2-3 microns to ~10 microns with a current density in the order of 105 A/cm2 which is around 10 times lower than that known for electro-migration damage. The dislocations and other defects in the as-received samples are absent in the resulted large-grain specimens. Currently we are testing the mechanical strength of resulted materials in comparison to the as-received ones. In the meanwhile, we are conducting conventional thermal annealing of the as-received specimen and comparing the results with that of electrical annealing.

10:30 AM - TC02.15.08

Development of and Initial Results from the First In Situ Ion Irradiation Dynamic TEM

Traditional in situ transmission electron microscopy (TEM) is capable of imaging structure and morphology, characterizing defects, and chemical analysis with high spatial resolution in a range of applied thermal, mechanical, and environmental loads, but is limited by the temporal resolution of the instrument. Advancement in both high speed direct detect cameras and Dynamic TEM (DTEM) have dramatically increased temporal resolution down through the sub-millisecond region to the nanosecond regime, respectively. In particular, the electron optics of DTEM has been developed to investigate materials under transient conditions with nanosecond temporal resolution through the use of a pulsed laser to generate short pulses of electrons from a photocathode source, and electrostatic deflectors to raster multi-frame images. We have expanded on the environmental conditions that can be studied at these spatial and temporal resolutions by combining the movie mode DTEM technology with the environmental control capabilities of the existing In-situ Ion Irradiation Transmission Electron Microscope (I3TEM) facility. This allows for investigation of materials in a range of overlapping extreme environments including radiation defect production, ion species implantation, gas and liquid interactions, temperature extremes, mechanical strain, fatigue, creep and various synchronized combinations thereof with high temporal resolution.

This talk will highlight the current status of the I3DTEM including: an improved movie mode deflector system and resulting image analysis techniques, an in-situ specimen drive laser, a single shot DTEM cathode laser, and continued I3TEM modifications. Preliminary results of in-situ characterization of materials using the modified I3TEM include imaging single ion strikes of Pt, Au, and Si thin films with 2.8 MeV heavy ions, laser sintering of Cu nanoparticles, and rapid grain growth and texture evolution of PtAu thin films heated by the 1064 nm specimen drive laser.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Semiconductor thin films are often deposited amorphous and processed using laser induced crystallization for applications such as solar cells, IR detectors, and digital displays. For germanium under certain conditions, the crystallization front will undergo unsteady propagation, leading to a periodic microstructure that is not yet well understood. Here, we present the results of using Movie-Mode Dynamic Transmission Electron Microscopy (MM-DTEM) to characterize the unsteady crystallization behavior. The high spatial and temporal resolution of this technique, revealed discrete bands (~1 µm wide) that propagate at ~10 m/s perpendicular to the net crystal growth direction. The net growth speed varied from ~1.3 m/s down to 0.2 m/s consistent with the number of active fronts decreasing with temperature. The resultant anisotropic microstructure was further explored using automated crystallographic orientation mapping. These findings support liquid mediated crystal growth and we will present a proposed mechanism that explains the observed behavior and periodic microstructure. This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering for FWP SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Next generation nuclear reactors require the cladding and structural alloys to withstand higher temperature and higher doses. There are several candidate materials that have been proposed, including the ones used in this study: Al-Co-Cr-Fe-Ni high-entropy alloys (HEA) with three compositions: Al0.3CoCrFeNi, Al0.5CoCrFeNi and Al0.7CoCrFeNi. The samples were prepared by casting followed by 50 hours homogenization at 1,250 C and further annealing. They represent several different microstructures and phases with single FCC and BCC/B2 phases. Our preliminary study was performed using in situ ion irradiation at 300 C at the Intermediate Voltage Electron Microscopy Tandem Facility (IVEM) facility using 1 MeV Kr ions at a dose rate of 10^16 ions/m2/sec to irradiate thin TEM foils of HEA up to 20 dpa, at temperatures from room temperature to 360°C. The results showed good irradiation resistance of the samples with good phase integrity and microstructure stability. Detailed analysis of the ion irradiated samples with different microstructure and composition provides a better understanding of the irradiation performance and indicates the good irradiation tolerance of a new design of Al-Co-Cr-Fe-Ni high entropy alloys. This also provides clearer guidance for further future neutron irradiations experiment.

11:15 AM - TC02.15.11

High Throughput Screening of Metastable Phase Formation Applied to Compositions on Gradient between Computationally Predicted Piezoelectrics

Piezoelectrics are important materials for a variety of applications including energy scavenging, low power sensing, and band pass filters in wireless communications. Computational searches for new piezoelectric materials have generated libraries of candidate materials, including metastable structures which have not yet been experimentally observed. However, these computational searches have difficulty calculating free energies of off-stoichiometry compositions in binary or ternary systems. Computational predictions have identified a similar metastable phase of both MnTiO3 and FeTiO3 as a potential piezoelectric, but little data exists on the relative energies of this phase vs the stable phase on the ternary oxide line between the two compounds. Metastable phase formation at a range of compositions between MnTiO3 and FeTiO3 is screened using a high throughput process of millisecond time scale annealing. Samples of different compositions, deposited as amorphous films by pulsed laser deposition, were laser spike annealed (LSA) using a lateral gradient (lgLSA) method. Resultant structures were identified using spatially resolved X-ray diffraction. Formation of the known stable and metastable phases is identified as a function of composition and annealing time and temperature. Additionally, previously unidentified metastable phases are reported as well as the composition and annealing conditions where they are found. The use of the lgLSA technique with composition spreads promises to dramatically accelerate discovery of metastable phases under conditions not readily available to computational techniques.

The widespread use of carbon nanotubes (CNTs) in consumer applications is currently limited by the inability to grow high quality CNTs in bulk quantities with selective physical properties. In order to increase CNT growth efficiency, it is imperative to understand why some catalysts grow tubes and others do not. Progress in elucidating this has been impeded by the difficulty in studying catalyst systems at the required time resolution. Unfortunately, conventional growth setups present difficulty in the integration of time resolved characterization techniques for on-demand and on-site metrology. As an alternate, several efforts have focused on establishing specialized in situ and in operando experimental platforms that can be used as a diagnostic tool for growth. A large body of in situ work has led to interesting findings concerning growth kinetics. For instance, environmental Transmission Electron Microscopy, in situ Raman and in situ GISAXS have been exploited to be used as diagnostic tools for CNT growth. These techniques have provided crucial knowledge regarding growth such as catalyst evolution –including dewetting and coarsening, Oswald ripening mechanisms, catalyst/support interactions, step flow and cap formation, multi-variable- dependent growth yield and lifetime, among others. However, these techniques lack the ability to simultaneously capture oxidation state and reaction kinetics. Ambient pressure-photoelectron spectroscopy (AP-PES), on the other hand, can be used to reproduce growth conditions while detecting the chemical state of the catalyst during catalyst evolution and detect nucleation and growth of a CNT at its early stage. In fact, this technique has been used to pin down the active catalyst state at the point of nucleation. In parallel to other in situ and in operando experimental techniques, AP-PES (also referred to as in situ X-ray Photoelectron Spectroscopy) can be used to attain control over key factors in growth such as catalytic yield and lifetime for scalable CNT synthesis. We expand on previous AP-PES work to further understand the active catalyst state for enhanced growth. Using the AP-PES end station (CSX-2 beamline) at the National Synchrotron Light Source II (NSLS II) in Brookhaven National Laboratory (BNL), we conducted a systematic study to monitor catalyst oxidation state and diagnose CNT growth. In doing so, we were able to assess how a catalyst system evolves and understand what factors determine when a catalyst grows or does not. The role of oxidation state of the catalyst and catalyst/support preconditioning were examined. A direct correlation between catalyst oxidation state, nucleation density and growth quality was observed. Reducing agents are presented as a key factor in increased nucleation density and growth yield. We propose a rationale for the reasons as to what factors may quench or enhance growth.